IWIVER6II, or '
THE NOMENCLATURE OF PETROLOGY
THE AGE OF THE EARTH.
Harper's Library of Living Thought.
HARPER BROS., LONDON AND NEW YORK.
THE GEOLOGICAL AND PHYSICAL CHARACTERS OF
"Red Book" No. 256.
BRITISH FIRE PREVENTION COMMITTEE, LONDON.
PETROGRAPHIC METHODS AND CALCULATIONS.
Ready in the early Autumn.
T. MURBY AND CO., LONDON.
WITH REFERENCES TO SELECTED LITERATURE
D.SC. (LOND.), A.R.C.S., D.I.C., F.G.S., F.R.G.S.
Demonstrator of Geology and Petrology in the Imperial College of Science and
Technical Geologist to the British Fire Prevention Committee
LONDON: THOS. MURBY & CO., i, FLEET LANE, E.G. 4
JSTEWYORK: D. VAN NOSTRAND CO., 8, WARREN STREET
GLOSSARY OF TERMS 23
APPENDICES - 243
A, French Petrographic Terms - - 243
B. German Petrographic Terms
(compiled by Miss J.-H. ROBERTSON) 247
C. Greek Words and Prefixes - 257
D. Latin Words and Prefixes - 263
E. Classification Tables - - - 265
THE NOMENCLATURE OF
SOME years ago I began the compilation of a card-
catalogue of petrographic and associated terms, for
the use of students in the Geological Department of
the Imperial College of Science and Technology.
Each card gave a brief description of the meaning
(or meanings) of the term to which it was devoted,
together with references to those papers on the sub-
ject which were available in the departmental
library of the College, a library which, thanks to
the collections made by the late Professor J. W.
Judd and others, is unusually rich in author's
separates. As the catalogue grew, its general use-
fulness became apparent; and a series of sugges-
tions that it should be developed and published led
me finally to the conclusion that such a course
would not be unjustified.
There are many geological glossaries in which
petrological terms find a place, but they are for the
most part old, and to-day they are but little used, or
2 THE NOMENCLATURE OF PETROLOGY
even 'known. 1 Several petrological books contain
glossaries; notably Sir Jethro Teall's great work,
British Petrography (1888), and J. R. Kemp's
Handbook of Rocks. The latest edition of Kemp's
book was published in 1918, and contains a wealth
of information, particularly in relation to the older
terms and the newer American terms. The only
independent publication of the kind, however,
appears to be the Lexique Petrographique of
-Lcewinson-Lessing (Paris, 1901). This invalu-
able work is now nearly twenty years old, and so
luxuriant has been the growth of nomenclature dur-
ing the last two decades, that the Lexique no longer
serves as an adequate guide through the somewhat
tangled forest of names.
The complexity of petrological nomenclature at
the present day is demonstrated by the following
list, in which examples are given to illustrate the
varying characters and principles on which names
have been based from time to time.
Classical : basalt, basanite, obsidian, porphyry, syenite.
Popular : chert, cokeite, forellenstein, gabbro, gneiss,
granite, greisen, halleflinta, loess, marl, minette.
Structure: augen-gneiss, banket, cipolino, dermolith, folia-
1 Among those examined for the purpose of this book are the
G. Roberts : An Etymological and Explanatory Dictionary
of the Terms and Language of Geology, 1839.
D. Page : Handbook of Geological Terms, 1859 & 1865.
W. Humble : Dictionary of Geology and Mineralogy, 3rd
G. H. Kinahan : A Handy Book of Rock Names, 1873.
B. von Cotta (Trans, by P. H. Lawrence) : Rocks Classified
and Described, 1878.
T. H. Oldham : Geological Glossary, 1879.
THE NOMENCLATURE OF PETROLOGY 3
tion, knotenschiefer, lithophysae, oolite, perlite, pudding-
stone, rhyolite, schist, variolite.
Texture : anamesite, aphanite, granulite, hornstone, lithoi-
dite, pegmatite, rhomb-porphyry.
Roughness : grit, trachyte.
Colour : eclogite, graywacke, greenstone, leucocratic, leuco-
phyre, melanocratic, melaphyre, muscovadite, troctolite.
Lustre : euphotide, lamprophyre, pitchstone.
Fusibility : eurite, pyromeride, tachylyte.
Organic characters: coral-sand, crinoidal limestone, diato-
mite, globigerina-ooze, lignite, miliolite.
Mineral characters : aplite, diorite ;
albitite, amphibolite, anorthosite, argillite, augitite,
hornblendite, quartzite, peridotite ;
albite-enstatite rock, anorthite rock, muscovite-rutile
rock, quartz-barytes rock ;
glauconitic sandstone, glaucophane-schist, hornblende-
granite, mica-schist, nepheline-syenite, olivine-basalt,
Chemical characters: alkali-rocks, anthracite, calc-alkali-
rocks, calc-flinta, calciphyre, picrite, soda-rhyolite.
Use : laterite, novaculite.
Mode of formation : crush-breccia, flow-breccia, mylonite,
Alteration : diabase, rapakivi.
Relative age : palasopicrite, proterobase, protogine.
Tribal names : gondite, ossypite.
Surnames : buchnerite, charnockite, dolomite, grahamite.
Place-names : cornubianite, ivernite, norite ;
andesite, bostonite, canadite, jacupirangite, laurdalite,
monchiquite, nevadite, sussexite, tonalite, wyomingite.
Hunne diabase, Markle basalt, Ponza trachyte.
Compound rock-names: granodiorite, rhyodacite, syeno.
Greek prefixes: apo-rhyolite, epidiorite, hyalobasalt, kata-
gneiss, micropegmatite, orthogneiss, paragneiss, pseudo-
4 THE NOMENCLATURE OF PETROLOGY
Greek suffixes: basanitoid, dacitoid, graneid, pegmatoid,
Mnemonics: felsic, femic, mafic, salic.
For many years the fashion has been established
of basing new rock-names on geographical names,
a method that burdens the memory with many ugly
and cacophonous terms, leads sometimes to re-
dundancy, and fails to suggest the distinctive
characters of the rock-types so described. It is
difficult, however, to see how these objections can
be altogether avoided. A different application of
the method has sometimes been made, a new type
being described partly in terms of a well-known
rock-name, and partly in terms of the locality where
the type-rock occurs. Thus we have Ponza
trachyte, Hunne diabase, and Markle basalt. More
purely descriptive names, formed by adding
mineral-prefixes to existing rock-names, such as
biotite-hornblende-granite, are self-explanatory;
and the same advantage is shared by compound
terms like granodiorite, trachyandesite, and melano.
cratic olivine-trachydolerite. There is much to be
said in favour of combinations of these kinds, as
they reduce the number of fundamental names to be
remembered, and are of wider application than
specific names. Many protests have been made
against the use of long compound-names, but,
unless they become ridiculously cumbrous, they are
thoroughly justified in the interests of clearness, as
they are, for example, in organic chemistry.
A geographical appellation already established,
such as lugarite or marloesite, should not be
THE NOMENCLATURE OF PETROLOGY 5
adopted for a rock from a fresh locality, unless the
identity of type so implied is sufficiently close to
avoid all chance of misconception. On the other
hand, a new name should not be resorted to until
every other possibility has been tested and found
inadequate. There is undoubtedly an attraction in
the creation of new names, and in too many cases
that attraction has not been dispelled by the verbal
discords eventually produced. On several occa-
sions in my own experience I have been inclined to
coin specific names. A riebeckite-asgirine granite
from Angola 1 was a temptation for a time, but fortu-
nately it was resisted. Otherwise our nomencla-
ture would have been burdened with two new and
unnecessary synonyms, for simultaneously Lacroix
described a similar rock from Madagascar 2 under
the name fasibitikite. In a case like this I consider
that three words are better than one. Brevity of
expression is by no means an unmixed blessing,
and the one word may require a whole paragraph of
It would, of course, be desirable if definitions of
rock-names could be framed by an International
Committee endowed with authority to fix meanings
finally, and to decide on the validity of new terms
at suitable intervals. Unfortunately such a counsel
of perfection is not likely to be sought for many
years, and even were a powerful committee to be
formed, its authority would sooner or later be
sapped by disagreement. One such attempt to
1 A. Holmes : Geol. Mag., 1915, p. 267.
2 C.R., clxi, 1915, p. 253.
6 THE NOMENCLATURE OF PETROLOGY
standardise nomenclature revealed so wide and
stubborn a divergency of opinion as to its prac-
ticability, and the individual rights of authors to
use terms as they choose, that no final decisions
were arrived at, and only a few general suggestions
and the revised Lexique of Lcewinson-Lessing
emerged from the conferences. 1 The authors of
the Quantitative Classification of Igneous Rocks
have summed up the position by a quotation so
happy that no apology is necessary for repeating it
" There's glory for you," said Hnmpty Dumpty.
" I don't know what you mean by glory," Alice said.
Humpty Dumpty smiled contemptuously. " Of course you
don't till I tell you. I meant there's a nice knock-down
argument for you !"
" But glory doesn't mean ' a nice knock-down argument,' "
" When / use a word," Humpty Dumpty said in rather a
scornful tone, " it means just what I choose it to mean
neither more nor less."
" The question is," said Alice, " whether you can make a
word mean so many different things."
" The question is," said Humpty Dumpty, " which is to be
master that's all."
Alice Through the Looking Glass (Lewis Carroll).
Two main difficulties stand in the way of uni-
versal agreement. One of these is the natural
tendency of words in active use to grow, and
1 Com-ptes Rendus, viii, Congres Geologique International,
Paris (1900), 1901.
2 W. Cross, J. P. Iddings, L. V. Pirsson, & H. S. Washing-
ton : Journ. Geol., xx, 1912, p. 559.
THE NOMENCLATURE OF PETROLOGY 7
gradually to assume a wider and therefore less pre-
cise meaning than that for which they were
originally intended; while in time they may come
to have a totally new, and at first sight quite un-
related, meaning. The standard petrological
example of a word illustrating this process is
porphyry ; and quite recently the term dedolomitisa-
tion began to extend its scope, though in this case
the tendency was thwarted by a timely protest. 1
Even in 1811 we find Pinkerton complaining in his
Petralogy that the term freestone, instead of being
restricted to "the noblest of the common lime-
stones," had been inaccurately applied to sand-
stones! He overcame this "abuse of language"
by proposing konite for the limestones so beloved
of the mediaeval freemasons. And introducing
another rock which he describes with great
enthusiasm, he writes, "This is the celebrated
pudding-stone of England, so much in request in
foreign countries; but this name commonly excit-
ing a smile among the illiterate, and the applica-
tion being since enlarged to a great number of
glutenites, 2 of a different nature and origin, form-
ing entire chains of mountains (while this is con-
fined to a very small district in England, and is
found nowhere else in the world), it has been
thought proper to distinguish it by the name of
Kollanite; derived from the Greek, denoting its
appearance of being cemented together."
1 Geol. Mag., 1919, p. 458.
2 A term, mow obsolete, for breccias, conglomerates, and
8 THE NOMENCLATURE OF PETROLOGY
The late A. D. Darbishire in his posthumous and
unfinished Introduction to a Biology (1917) dis-
cussed the wanderings of words in relation to a
subject where the danger is even greater than in
" If there is a possibility that words give a
semblance of progress in interpretation, where in
reality there is none, it is desirable that some atten-
tion should be paid to the relation between word
and thought. . . .
" A word and its meaning, especially in the case
of ideas, are united together by a slender, elastic
bond which is now contracted, now stretched to its
uttermost. ... So we see the word and its mean-
ing dancing to each other in an airy medium, like a
pair of gnats in the lee of a gorse-bush. This,
alas ! is the simplest case. The more complicated
and much more common cases are those in which
one word has more than one meaning, or where one
meaning has more than one word to express it;
these are the cases which, in verbal life, are pro-
ductive of trouble " (pp. 19-21).
Such difficulties are sometimes accentuated by
human perversity : witness Rosenbusch's treat-
ment of Vogelsang's term granophyre, and
Brogger's appropriation of foyaite and ditroite.
Consider also the introduction of the terms aa and
aphrolith to denote the qualities already simply ex-
pressed by block-lava-, and of midalkalite and
syenoid to take the place of nepheline-syenite.
The second difficulty standing in the way of
agreement is intimately related to the first.
THE NOMENCLATURE OF PETROLOGY 9
Although petrology is now developing rapidly, no
generally accepted classifications of the major
groups of rocks have yet been devised with suffi-
cient detail to guide the choice of terminology and
to restrain its tendency to spread outwards and be-
come confused. Existing classifications involve a
and chemical composition, proportions of minerals,
and chemical composition, proportions of minerals,
structure, texture, mode of occurrence, degree of
alteration, etc. and any given name is therefore
liable to wander in various directions according as
insistence is placed on one or other of its possible
connotations. A successful classification will need
to be sufficiently elastic to avoid the despotism of
merely arbitrary and unsignificant division, and
yet sufficiently rigid to standardise the meanings of
its collateral terminology.
At the present time the field of petrology still
contains many uncultivated corners, and until the
whole has become familiar ground, existing
systems of classification and nomenclature must be
regarded as on probation. It is my impression that
stability will be approached, not primarily as a
result of any committee, international or sectional,
but by the co-ordinating work of a single petrolo-
gist of genius whose authority, the outcome of his
own success and influence, will be far superior to
the merely temporising and democratic authority
of a committee.
Meanwhile it seems desirable to take stock, and
to place on record the existing nomenclature in
accordance with its current usage. It is hoped that
io THE NOMENCLATURE OF PETROLOGY
this book will meet the need by creating a standard
of reference which may to some extent limit future
vacillations, and prevent unnecessary clashing
between new terms. The main object of the book
is, however, to be practically useful by serving as a
guide to student, teacher, research-worker, and
professional geologist, and indeed to all who need
to follow petrological literature or to contribute to
The work involved in revising and amplifying
the original card-catalogue, undertaken about a
year ago, proved to be more arduous than
was at first anticipated. It has, however, never
descended to drudgery or mere compilation. On
the contrary it has been in the nature of a literary
exploration, leading one to examine a century's
evolution of petrological thought and method, and
to share the delights of many a curious traveller
through little-known corners of lands the world
over. Unsatisfactory though certain parts of the
nomenclature may be as an instrument of thought
and exposition, it is, as a w^hole, unusually rich in
pleasant associations, geographical, historical, and
even psychological. Perhaps this romantic aspect
of a subject bristling with technicalities is a dan-
gerous one, for it tends to support the natural con-
servatism of even scientific men, and so, perhaps,
to retard the development of that ideal system of
nomenclature which we all hope for but cannot as
Certain attempts to systematise nomenclature
have already been made, particularly in the field of
THE NOMENCLATURE OF PETROLOGY n
igneous rocks. It is desirable to draw attention to
some of these, because, with a few exceptions, the
terms they comprise have been excluded from the
glossary that follows.
Jevons suggested a wholesale use of prefixes con-
sisting of contracted, or rather mutilated, forms of
structural, textural, and mineral names, together
with a few chemical and qualifying syllables. 1 He
thus arrived at such combinations as ophit-oli-
dolerite, diopsi-mipegmo-rhyolite, rhomfels-pyr-
alisyenite ( = Laurvikite), and eud&gi-midalkalite
( = Lujaurite). Such proposals are obviously fore-
doomed to failure. In the words of Professor
Bonney, "Time is not so valuable, or paper and
printing so expensive, that we should talk or write
4 gibberish ' to save a few letters."
A more reasonable method has recently been
proppsed by Professor Shand, 2 based in its applica-
tion on the classification of igneous rocks according
to his principle of saturation. 3 He suggests
(1) That the names of oversaturated and saturated
rocks should end in the customary suffix -He ; e.g.,
granite, syenite, etc.;
(2) That the names of unsaturated rocks should
(a) the prefix sub-, or the suffix -ole, to indicate
that the dyad or triad metals are unsaturated ;
e.g., subgabbro, for olivine-gabbro ;
(b) the suffix -oid, to indicate that the monad
1 H. S. Jevons : GeoL Mag., 1901, p. 304.
2 S. J. Shand : Geol. Mag., 1917, p. 466.
3 GeoL Mag., 1913, p. 508; 1914, p. 485; 1917, p. 115.
12 THE NOMENCLATURE OF PETROLOGY
metals are unsaturated; e.g., syenoid, for
nepheline-syenite ; and
(c) a combination of the prefix sub- and the
suffix -old, to indicate that both monad and
dyad metals are unsaturated, e.g., subthera-
loid or subgabbroid, for olivine-theralite.
The principle adopted is excellent, but the choice
of suffix, -aid, is unfortunate and cannot be
accepted, for it has already been seriously over-
worked in other directions. It has been used in
adjectival terms like granitoid and trachytoid, tc-
express texture or composition ; and in substantive
form in the term pegmatoid, to denote very coarse-
grained facies of igneous rocks differing from peg-
matite proper by the absence of graphic-texture;
and in terms of which dacitoid is a typical example,
to connote similarity (to dacite) of chemical com-
position combined with dissimilarity of mineral
The authors of the Quantitative Classification
have introduced a very comprehensive nomencla-
ture, the greater part of which is built up with the
aid of a variety of suffixes and mnemonic contrac-
tions. Terms like felsic and mafic are extremely
useful, and even though they have been regarded
as technical slang, they have justified their inven-
tion by having been widely adopted. On the other
hand, more ambitious and less useful terms such as
alferfemphyric are ugly and have not met with a
similar measure of favour. Cross, Iddings,
Pirsson and Washington 1 have themselves made
1 These authors are referred to in the glossary by CJ.P.W,
THE NOMENCLATURE OF PETROLOGY 13
the recognition of much of their nomenclature a
necessity, for they have forcibly and persistently
made use of it in a long series of publications which
other petrologists cannot afford to ignore. Most of
the new terminology, however, is intimately related
to, and only used in connection with, the Classifica-
tion itself, and with the latter it must therefore stand
or fall. Unfortunately, the principles on which the
Classification is based leave the main problems of
petrology untouched, fail to open out new fields of
research, and therefore do not constitute a creative
contribution to the subject they were intended to
illuminate. From this point of view the apparently
wide influence exerted by the Classification in
recent years has been largely factitious. Neverthe-
less, it is only fair to add that the authors of the
Classification have rendered very real services to
petrology by promoting greater accuracy of
description and analysis, and by introducing the
conception of the norm, which provides an admir-
able method of recalculating, comparing, and inter-
Another systematic terminology to which refer-
ence must be made has he_en proposed and exten-
sively used by Grabau in his Principles of Strati-
graphy (1913). The terms are summarised on
pp. 296-7 of that work, and constitute an attempt,
laudable in principle, to provide a comprehensive
nomenclature for sedimentary and associated rocks.
By means of a number of prefixes representing
chemical or mineral composition and agency of
formation, compound terms are built up at will by
i 4 THE NOMENCLATURE OF PETROLOGY
combining them with a series of grade designa-
tions : rudyte, corresponding to gravel, shingle,
pebbles, etc.; ar&nyte, corresponding to sand; and
lutyte, corresponding to mud or rock-flour. Thus
anemoarenyte in ordinary terms would be described
as asolian sand; hydrosilicirudyte as quartz-con-
glomerate; and pyrolutyte as volcanic ash or
dust. The extent of departure from current
nomenclature is unnecessarily wide, and it seems
doubtful whether such innovations will ever be
recognised by adoption. Grabau's use of the terms
exogenetic and endogenetic is particularly unfortu-
nate and tends to confusion of thought. 1 He
describes rocks as "exogenetic" when they have
been formed by agents acting from without, that is,
acting externally with respect to, and indepen-
dently of, the finished rock, as in the case of loose
detrital sediments. Other rocks, formed by agents
acting from within, he describes as "endogenetic,"
this category including igneous rocks, saline
deposits, and organic accumulations. The two
contrasting terms, although they are applied to
rocks, are thus made to be synonymous with
allo genie and authigenic respectively, and as the
latter terms lead to a far clearer realisation of the
primary division proposed by Grabau there seems
to be no reason for rejecting them. The sentence
" A calcareous sandstone contains allogenic grains
held together by an authigenic cement," gives an
accurate statement of fact, whereas the classifica-
1 Amer, Geol., xxxiii, 1904, p. 228,
THE NOMENCLATURE OF PETROLOGY 15
tion of a calcareous sandstone as " exogenetic " in
Grabau's sense expresses only part of the truth.
The obvious and most serviceable meanings of
exogenetic and endogenetic are those proposed by
Mr. T. Crook, 1 and they should be adopted and
used as defined by him. Exogenetic applies
to processes originating and operating at or near
the earth's surface, and to the rocks and ore-
deposits formed by such processes. Endogenetic
applies to processes originating internally and
operating deep-seatedly in the earth's crust, or from
within outwards, and to the rocks and ore-deposits
formed by such processes.
If it be objected that Grabau has priority as re-
gards date of publication, the reasons for rejecting
his usage would be based on the following points
(a) The French equivalents of the terms,
exogene and endogene, have long been used
to express the division of rocks into ' * erup-
tive " and " sedimentary " groups.
(b) Reference to Murray's Oxford Dictionary
will show that exogenetic had previously
been recognised in the sense followed by
(c) Grabau has used the terms for a concep-
tion which they fail adequately to express,
and for which wholly adequate terms were
Only one of Grabau's terms, rudaceous, has been
included in the glossary, because with arenaceous
1 " The genetic classification of rocks and ore deposits,''
Min. Mag. t xvii, 1914, p. 72.
16 THE NOMENCLATURE OF PETROLOGY
and argillaceous, it completes a Latin trilogy for
the three main groups of detrital sediments. As
far as I know there has not hitherto been a term of
Latin form for coarsely graded detritus of the kind
which is described in the corresponding Greek
trilogy as Psephitic.
Several of the Cross-Iddings-Pirsson-Washing-
ton terms have been incorporated, including a
selection of the chief key-words and prefixes of the
nomenclature associated with the divisions of the
classification . The greater part of that terminology
has been excluded, and those wishing to become
familiar with its details are referred to the various
publications cited below. 1
In addition to the excluded terms already referred
to, certain others have also been omitted :
(a) Modifications of existing terms such as
Johannsen's 2 field terms, graneid, dolereid,
anameseid porphyry, etc.; and Dana's 3 and
Graubau's 4 terms ending in -yte instead of
(b) Most compound terms built up from
mineral qualifiers. These are, of course, in-
1 C.I.P.W. : Journ. GeoL, x, 1902, pp. 555-690.
Quantitative Classification of Igneous Rocks, Chicago,
1903. (Glossary on pp. 261-284.)
J. P. Iddings : Igneous Rocks, I, 1909, pp. 394-454.
C.I.P.W. : Journ. GeoL, xx, 1912, pp. 550-561.
G. I. F inlay : Introduction to the Study of Igneous Rocks,
1913, pp. 143-221.
H. S. Washington : Chemical Analyses of Igneous Rocks
(U.S.G.S. Prof. Pap., 99). 1917, pp. 1151-1161.
2 A. Johannsen : Journ. Geol., xix, ign, p. 317.
3 J. D. Dana : Am. Journ. Sci. and Art, xvi, 1879, p. 336.
4 A. W. Grabau : Principles of Stratigraphy, 1913, p. 298.
THE NOMENCLATURE OF PETROLOGY 17
numerable and would unnecessarily over-
burden the glossary. 1 Where the qualifier
has become an essential part of the name of
an important group of rocks, as in quartz-
diorite, nepheline-syenite, chlorite-schist,
etc., the resulting term has, however, been
(c) Most obsolete terms, such as those proposed
by Pinkerton in his Petrology. Two of
these, konite and kollanile, have already been
mentioned. A few terms that have more
recently fallen into desuetude are introduced,
partly to indicate the reason for their obsoles-
cence and partly because they may be met
with in literature that has not yet been super-
With these exceptions the glossary forming the
greater part of this book is believed to be reason-
ably complete. The general treatment is his-
torical rather than critical, the main object
being to record the customary current mean-
ing of each term, together with the original
author and the date of its first use, and
in the case of rock-names the type-locality. It has
been no part of my purpose either to recommend or
discourage the use of any recognised term, and
throughout I have abstained from discussing either
the value of a term, or the need for it. A critical
examination of terminology could be conducted
more satisfactorily from the standpoint of classifica-
1 See also J. D. Dana : Am. Journ. Sci., xxxii, 1886, p. 71.
i8 THE NOMENCLATURE OF PETROLOGY
As will be seen from the glossary itself, the terms
incorporated include not only those describing
rocks, structural and textural features, modes of
occurrence, and processes, but also a selection of
terms associated with petrographic methods, most
terms referring to crystal optics and physics
being excluded. In the case of terms denoting the
mode of occurrence of igneous rocks (e.g. batholith)
it seemed desirable to introduce a uniform ending
-lith throughout. Thus, instead of Gilbert's lacco-
lite and Marker's phacolite, the forms laccolith and
phacolith have been adopted. This course serves
to distinguish such names from mineral and rock
names, and in the case of phacolith it avoids
possible confusion with the zeolite phacolite. Dr.
Harker, who has hitherto used the ending -ite,
raises no active objection to the change suggested.
In the case of the mineral names cegirine,
nepheline, nosean, hauyne, the form of spelling
here given has been retained, but analcime has
been allowed to yield to analcite. The original and
more harmonious termination was given by Haiiy
in 1801, but the more systematic ending adopted
by Galitzin, also in 1801, seems to have achieved
greater currency. Moreover, the latter form has
been fixed by the rock-name analcitite, whereas it
is nepheline and not nephelite that is fixed by the
corresponding rock-name nephelinite.
Selected references to the literature of the respec-
tive subjects have been appended to many of the
items of the glossary. The choice of reference has
not always been easy. It is manifestly impossible
THE NOMENCLATURE OF PETROLOGY 19
to give a complete series of references in the case
of the older terms, and to give the original refer-
ences alone is neither desirable nor necessary, as
they are already available in Lcewinson-Lessing's
Lexique. The guiding principle has been to draw
attention to recent and readily accessible papers
which in turn serve to open out the older literature.
Had it been followed rigidly this course would have
led to the exclusion of many of the important papers
which we owe to the pioneers and veterans of petro-
logical research, and it would then have appeared
that the authors alluded to had been unduly
neglected. For this reason occasional references to
the older papers have been inserted in appropriate
For the literature dealing with the igneous
geology of particular districts the second part of
Iddings' Igneous Rocks, Vol. II., is the most
accessible source; while for individual rock-types
the copious references given in Washington's tables
of chemical analyses 1 cover the whole field up to
Appendices giving French and German words
have been added as a help to students reading petro-
logical literature in these languages. 2 Terms of
an international character, and words which are
readily recognised by their similarity to the Eng-
1 U.S.G.S., Prof. Pa-p. 99, 1917.
2 A useful dictionary for scientific purposes is A German-
English Dictionary for Chemists, by A. M. Patterson,
1917, as it contains an ample general vocabulary in addi-
tion to the technical terms of chemistry and related
20 THE NOMENCLATURE OF PETROLOGY
lish equivalents have been omitted. The German
appendix has been compiled by Miss J. H. Robert-
son, for whose help I wish here to acknowledge my
gratitude. Appendices setting forth Greek and
Latin words have also been added in order to make
clear the significance of the many petrographical
and mineralogical terms into which they enter.
Classification Tables have been introduced in
order to bring together terms representing closely
related concepts. These will be found useful not
only in taking a broad survey of certain parts of the
subject, but also in serving as a guide to new or for-
gotten terms. The tables also bring out the
" patchiness " of petrological nomenclature. Cer-
tain parts of the subject are heavily burdened with
redundant terms, and with others that depend for
their justification on differences so slight or trivial
that they have but little practical value. Other
parts of the subject, particularly those involv-
ing altered and metamorphic rocks have still a
somewhat restricted nomenclature. This is prob-
ably due to the fact that until recent years attention
had been focussed almost exclusively on igneous
rocks, with the result that petrology has developed
somewhat unequally. Fortunately the outlook is
gradually widening, and even ore-deposits and
meteorites are beginning to take a recognised place
in the subject to which they properly belong.
In the hope of making the glossary as representa-
tive as possible of customary modern usage, twenty
preliminary proofs were pulled and sent to various
THE NOMENCLATURE OF PETROLOGY 21
petrologists with a view to eliciting sugges-
tions, comments, and constructive criticism. This
plan proved highly successful, and a very valuable
series of replies was received from the following
gentlemen : Prof. T. G. Bonney, Prof. P. G. H.
Boswell, Mr. Alfred Brammall, Prof. Grenville A.
J. Cole, Prof. A. Hubert Cox, Mr. T. Crook, Dr.
J. V. Elsden, Dr. J. W. Evans, Mr. J. F. N.
Green, Dr. A. Harker, Dr. W. R. Jones, Prof. A.
Lacroix, Dr. G. T. Prior, Prof. P. Quensel, Mr.
W. Campbell Smith, Sir Jethro Teall, Dr. H. H.
Thomas, Mr. G. W. Tyrrell and Prof. W. W.
Watts. To all these I owe my heartiest thanks for
their very substantial help in bringing to com-
pletion my self-appointed task. As a result of
their approval of the project itself, and their active
assistance in suggesting additions and modifica-
tions, I am supported in my belief that the book
will meet a real need, and encouraged in my hope
that the design originally conceived may have been
brought to a successful issue.
Finally, I wish to invite the further aid of those
who use the glossary, by asking them to acquaint
me with the particulars of any errors of interpreta-
tion or reference that may be detected, and to sug-
gest any additional terms that have unwittingly
been overlooked. Should the opportunity arise,
such corrections will be incorporated in a revised
edition, and as the "completion" of a glossary
such as this is necessarily relative to the date of
publication, authors of new terms are invited to
22 THE NOMENCLATURE OF PETROLOGY
ensure their future inclusion by communicating
with me either directly, or, if necessary, through
Imperial College of Science and Technology,
South Kensington, S.W.7,
THE NOMENCLATURE OF PETROLOGY 23
Aa, Dutton, 1883. A Hawaian term for block-lava,
consisting generally of a rough tumultuous assem-
blage of clinker-like scoriaceous masses. =Aphro-
lithic lava. Cf. Pahoehoe.
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 291.
J. A. Jaggar : Journ. W ash. Acad. Sci., vii, 1917.
Aasby Diabase, Tornebohm, 1877. A type of olivine-
dolerite containing biotite, ilmenite, and apatite,
in addition to'labradorite, augite and olivine.
Absarokite, ladings, 1895. A porphyritic, basaltic or
trachy-doleritic rock, characterised by the presence
of phenocrysts of olivine, augite, and labradorite
in a base containing orthoclase-mantled labra-
dorite. (Absaroka Range, Yellowstone Park.)
J. P. Iddings: Journ. GeoL, iii, 1895, p. 938.
U.S.G.S., Mon., xxxii (ii), 1899, p. 328.
Abyssal Assimilation, Daly. See Assimilation.
Abyssal Injection, Daly, 1906. The process whereby
magmas originating at considerable depths are
considered to have been driven up through deep-
seated contraction-fissures in the earth's crust.
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 174.
Abyssal Rocks, Brogger. A general term for rocks
of major intrusions. Cf. Plutonic.
Accessory. A term applied to minerals occurring in
small quantities in a rock, and whose presence
or absence does not affect its diagnosis.
R. H. Rastall & W. H. Wilcockson : QJ.G.S., Ixxi, 1915,
P. G. H. Boswell: GeoL Mag., 1916, p. 165.
24 . THE NOMENCLATURE OF PETROLOGY
Accidental Inclusions, Harker, 1900. A term applied
to xenocrysts or xenoliths having no genetic con-
nection with the igneous rocks in which they oc-
cur ; = enclaves enallo genes.
A. Harker: Journ. GeoL, viii, 1900, p. 389.
Achondrite, Cohen. A general term for stony meteo-
rites (aerolites) free from the spheroidal structures
known as chondrules. Cf. Chondrite.
Acid- A term applied to igneous rocks having a
higher percentage of silica than orthoclase, the
limiting figure commonly adopted being 66 per
cent. Cf. Persilicic and Over saturated.
Adamellite, Cathrein, 1890. A term applied origin-
ally to an orthoclase-bearing tonalite, and now
used generally for granites in which plagioclase
varies from one-third to two-thirds of the total
felspar. = Quartz-monzonite.
(Mt. Adamello, Tyrol.)
W. C. Brogger : Eru-ptivgesl. Kristiania, ii, 1895, p. 61.
Adinole, Haus smarm, 1847. A contact modification
of shale or slate metamorphosed and albitised by
doleritic (albite-diabase) intrusions ; consists of a
mosaic of albite, or albite and quartz, with inter-
stitial chlorite and iron-ores.
H. Dewey : Trans. Roy. Geol. Soc. Cornwall, xv, 1915, p. 71.
Adobe, Russell, 1889. A loess-like deposit occurring
in the plains and basins of the Western States, and
in the arid parts of Spanish America.
Adsorption. A term applied to the change in con-
centration of solutions and colloids where they
come into contact with surfaces.
Aeolian. A term applied to deposits whose constit-
uents have been carried by, and laid down from,
S. C. Stuntz & E. E. Free : U.S.A. De-pt. Agriculture, Bureau
of Soils, Butt. 68.
Aerolite. A general term for meteoric stones, that is
for meteorites composed mainly of silicates such as
pyroxenes and olivine, with or without small quan-
tities of nickel-iron, troilite, etc. According as
THE NOMENCLATURE OF PETROLOGY 25
chondrules are present or absent, aerolites are
divided into chondrites and achondrites (q-v.).
Agglomerate, Lyell, 1831. A chaotic assemblage of
coarse angular pyroclastic materials.
Aggregate Polarisation. The mottled appearance
seen between crossed nicols of a mineral aggregate
composed of minute particles which are orientated
Agpaite, Ussing, 1911. A general term applied to the
felspathoidal rocks of Ilimansak, Greenland, and
including sodalite-foyaite, naujaite, lujaurite, and
N. V. Ussing : Medd. om. Grdnland, xxxviii, 1911.
Jlsyte, Heddle, 1897. A variety of riebeckite micro-
granite, or paisanite. (Ailsa Craig.)
. 1. J. H. Teall : Min. Mag., ix, 1891, p. 219.
.kerite, Broggcr, 1890. A variety of quartziferous
augite-syenite, containing soda-microcline and
oligoclase. (Aker, Norway.)
W. C. Brogger : Eru-ptivgest. Kristiania, ii, 1895, p. 43.
Alaskite, Spurr, 1900. A leucocratic granite, contain-
ing quartz and alkali-felspars, with only traces of
other minerals. (Alaska.)
J. E. Spurr : Amer. GeoL, xxv, 1900, p. 231.
Hlbertite, How, 1860. A black variety of bitumen
with a brilliant lustre and conchoidal fracture.
H = i 2 ; S.G. about i.i. It differs from manjak
and uintaite by being practically insoluble in alco-
hol, and only partly so in turpentine.
(Albert Mines, New Brunswick.)
Albite-diabase. An altered and albitised doleritic
rock, containing albite in place of the usual plagio-
clase ; purple brown augite more or less replaced
by epidote, chlorite, and calcite, and titaniferous
magnetite ; the intrusive equivalent of spilite.
H. Dewey & J. S. Flett : GeoL Mag., 1911, p. 202.
Albite-enstatite Rock, Els den, 1905. A local fades,
possibly aplitic, of the enstatite-diorite of Pen-
clegyr. (Forth Gain, Pembroke.)
J. V. Elsden : Q.J.G.S., Ixi, 1905, p. 579.
26 THE NOMENCLATURE OF PETROLOGY
Albitisation. The process, due to paulopost juvenile
action, whereby the plagioclase (originally richer
in anorthite) of igneous rocks is replaced by albite ;
e.g., in spilite.
E. B. Bailey & G. W. Grabham : Geol. Mag., 1909, p. 250
H. Dewey & J. S. Flett : Geol. Mag., 1911, p. 202.
N. Sundius : Geol. For. i Stockholm Fork., xxxiv, 1912,
P- 3 1 ?-
Albitite, Turner, 1896. A leucocratic soda-syenite or
porphyry composed almost wholly of albite.
H. W. Turner : U.S.G.S. i^th Ann. Rep., ii, 1896, p. 477,
Albitophyre, Coquand, 1857. A porphyry in which
the felspar phenocrysts and the microlites of .he
groundmass are chiefly albite. Cf. Orthophyre. ^_
A. Holmes : Geol. Mag., 1917, p. 403.
Alboranite, Becke, 1899. A variety of ' ' hypersthenv
andesite," containing plagioclase at least as cal^ifl
as labradorite ; i.e., hypersthene-basalt with
microlitic texture like that of an andesite. \
(Alboran Is., Spain.'
Aleutite, Spurr, 1900. A term suggested for porphy-
ritic varieties of belugite (rocks intermediate
between diorite and gabbro) having an aphanitic or
finely crystalline groundmass. (Aleutian Is.)
J. E. Spurr : U.S.G.S., 2oth Ann. Re-p., Pt. vii, 1900, p. 195.
Algovite, W inkier, 1859. A group-term for a series of
augite-plagioclase rocks ranging from dolerite
through porphyritic varieties to gabbro.
Alkali Rocks. -- Igneous rocks in which the abund-
ance of alkalies in relation to other constituents
has impressed a distinctive mineralogical char-
acter ; generally indicated by the presence of soda
pyroxenes, soda amphiboles, and/or felspathoids.
Cf. Calc-alkali Rocks.
A. Lacroix : Nouv. Arch. Mus. cVHist. Nat., iv, 1902, p. 178.
G. T. Prior : Min. Mag., xiii, 1903, p. 254.
A. Harker : Nat. Hist. 1 g. Rocks, 1909, p. 90.
N. L. Bowen : Journ. Geol., Supp. to xxiii, 1915, p. 55.
A. Holmes : Q.J.G.S., Ixxii, 1916, pp. 268, 272.
R. A. Daly : Journ. Geol., xxvi, 1918, p. 97.
THE NOMENCLATURE OF PETROLOGY 27
Allalinite, Rosenbusch, 1895. A term applied to com-
pletely altered gabbros, the secondary minerals of
which smarag-dite, actinolite, and saussuritic
aggregates still occur as idiomorphic pseudo-
morphs after the original minerals, the initial tex-
ture of the rock being- thus retained. Contrasted
with flaser-gabbro, in which metamorphism has in-
volved structural as well as mineralogical changes.
(Allalin, near Zermatt.)
Allivalite, Harker, 1908. A phanerocrystalline rock,
consisting of anorthite and olivine in approxi-
mately equal proportions, or with felspar pre-
ponderating-. (Allival, Rum.)
A. Harker : Mem. Geol. Surv. Scot., 60 (Small Isles), 1908,
Allochetite, Ippen, 1903. - - A microlitic dyke rock
with phenocrysts of labradorite, orthoclase, nephe-
line and augite in a groundmass of felsic minerals
with augite and hornblende. (Allochet, Monzonj.)
J. A. Tppen : Verliandl. d. K.K. Geol. Rcichs., Wien, 1903,
Allochthonous, G umbel, 1888. - - A term applied to
rocks of which the dominant constituents have not
been formed in situ. Cf. Autochthonous.
Allothigenous, or AHogenic, Kalkovsky, 1880.
Terms, meaning- generated elsewhere, applied
to those constituents that came into existence out-
side of, and previously to, the rock of which they
now constitute a part; e.g., the pebbles of a con-
glomerate. Cf. Authigenous.
Allotriornorphic, Rosenbusch, 1887. A term applied
to those minerals of igneous rocks which are not
bounded by their characteristic crystal faces. =
Anhedral = Xenomorphic.
AHotropy. A term denoting the capacity of an
element to exist in more than one form while in
the same state; e.g., graphite and diamond,
orthorhombic and monoclinic sulphur, oxygen and
28 THE NOMENCLATURE OF PETROLOGY
A similar phenomenon is exhibited by many
compounds, und is then generally known as
dimorphism or polymorphism, though the term
allotropy has also been extended to cover such
cases, e.g. , the a, j8, and 7 forms of zircon, readily
distinguished by their specific gravities.
For a discussion of allotropy in relation to rock magmas
see W. H. Goodchild, Mining Mag., xviii, 1918, p. 243.
Alluvium. A general term for all detrital deposits "re-
sulting from the operations of modern rivers, thus
including the sediments laid down in river-beds,
flood-plains, lakes, fans at the foot of mountain
slopes, and estuaries.
Alphitite, Salomon, 1915. A term suggested for clays
consisting largely of rock-flour, such as those
washed and laid down from glacial debris.
W. Salomon : Geol. Rund., vi, 1915, p. 398.
Alnoite, Rosenbusch, 1887. A dyke-rock, containing
phenocrysts of biotite, olivine and augite in a
groundmass composed of melilite and augite, w'ith
sometimes perovskite, and other accessories. By
increase of melilite alnoite passes into melilite-
basalt. (Alno, Sweden.}
F. D. Adams : Ajit. Journ. Sci., xliii, 1892, p. 269.
J. S. Flett : Trans. Roy. Soc. Edin., xxxix, 1900, p. 891.
Alsbachite, Chelius, 1892. A porphyritic variety of
aplite, sometimes containing garnet.
Alum-shale. -- A shale impregnated with alum, the
latter constituent being due to the action on
sericite of sulphuric acid produced by the oxida-
tion and hydration of pyrite.
Ambonite, Verbeck, 1905. A variety of hornblende-
biotite-andesite characterised by the presence of
cordierite. (Ambon Is., Moluccas.)
Amherstite, Watson & Taber, 1913. -- A variety of
syenodiorite containing andesine-antiperthite.
(Amherst Co., Virginia.)
T. L. Watson & S. Taber : Geol. Snrv. Virginia, Bull. 3 A,
THE NOMENCLATURE OF PETROLOGY 29
Amorphous. A term applied to substances which are
not known to possess the discontinuous vector! al
properties or the periodic arrangement of com-
ponent atoms that characterise the crystalline
A. F. Rogers : Journ. GeoL, xxv, 1917, p. 515.
Ampelite. A general term for black bituminous or
carbonaceous shales, often pyritic.
Amphibole-magnetite Rock. A granulose often
banded rock containing- grunerite and other fer-
ruginous silicates, and magnetite, produced by the
contact metamorphism of ferruginous cherts
(taconite, jaspillite, etc.).
C. R. Van Rise C. K. Leith : U.S.G.S., Mon., Hi, 1911,
PP- 55. 55 8 -
Amphibolite, Brongniart, 1827. A granulose or
glomero-blastic metamorphic rock, consisting
essentially of amphibole and plagioclase, and
often containing quartz, epidote, or garnet.
G. A. J. Cole : Trans. Roy. Irish Ac ad., xxxi, 1900, p. 460.
J. J. H. Teall : Mem. GeoL Surv. (N.W. Highlands), 1907,
P. 5 6 -
F. D. Adams : Journ. GeoL, xvii, 1909, p. i.
P. Eskola : Bull. Comm. GeoL Finlande, No. 40, p. 97.
A. Holmes : Q.J.G.S., Ixxiv, 1918, p. 58.
F. L. Stillwell : Aust. Ant. Ex-ped. Sci. Rep. A, iii, I (i),
(Met. Rocks, Adelie Land), 1918, p. 24, etc.
Amphibololite, Lacroix, 1894. A general designation
for phanerocrystalline igneous rocks entirely or
almost entirely composed of amphiboles.
A. Lacroix : Now. Arch, du Mits. d'Hist. Nat., vi, 1894, p.
Amphoterite, Tschermak, 1683. -- An achondritic
meteorite composed essentially of bronzite and
olivine, with small amounts of oligoclase and iron
rich in nickel.
Amygdales or Amygdules. -- Vesicles or vapour
cavities of volcanic and occasionally of intrusive
rocks, which have become filled with secretionary
products (usually of late-magmatic origin), such as
zeolites, chlorite, forms of silica and calcite. The
30 THE NOMENCLATURE OF PETROLOGY
form amygdule is a diminutive of amygd&le, and
consequently the former is not strictly synonymous
with the latter.
W. F. P. McLintock : Trans. Roy. Soc. Edin., li, Pt. i,
iQi.5, P. T 3-
A. Holmes : Q.J.G.S., Ixxii, 1916, p. 251.
Amygdaloid. A general group-name for those vol-
canic rocks (andesites, basalts, etc.) which are
characterised by the presence of conspicuous
Amygdaloidal. A term applied to rocks containing
amvgdales, and to the structure resulting- from
Anabohitsite, Lacroix, 1914. A variety of olivine-
pyroxenite, containing- hypersthene and horn-
blende, with a high proportion of magnetite and/
or ilmenite. (Anabohitsy, Madagascar.)
A. Lacroix : C.R., clix, 1914, p. 419.
Analcite-basalt, Lindgren, 1890. An olivine-bearing
basaltic rock, in which the predominant felsic
mineral is analcite ; felspar, if present, being
merely accessory. Cf. leucite -basalt and rteph-
H. S. Washington : Journ. Geol., xvii, 1914, P- 742.
Analcite-dolerite. A dolerite, containing- analcite,
usually as an interstitial constituent. The term is
often used synonymously with Teschenite, but it
is preferable to employ the latter term only for
varieties containing- soda-pyroxenes and/or soda-
amphiboles. Cf. Crinanite.
Analcitisation, Flett, . 1900. - - The replacement of
felspars or felspathoids by analcite by late or post-
A. Scott : Trans. Geol. Soc. Glasgow, xvi, 1915-6, p. 34.
Analcitite, Pirsson, 1896. A term applied to rocks
which differ from analcite-basalt only by the
absence of olivine. Cf. leucitite and nephelinite.
Anamesite, Leorihard, 1832. A term meaning- inter-
mediate, applied to basaltic rocks that are of
coarser grain than aphanitic basalts, and of finer
THE NOMENCLATURE OF PETROLOGY 31
grain than those dolerites in which the individual
minerals can be megascopically distinguished.
Anamorphism, Van Hise f 1904. - - The constructive
metamorphism of rocks, characterised by the
formation of complex minerals at the expense of
C. R. Van Hise : U.S.G.S. Mon. 47, 1904.
C. K. Leith & W. T. Mead : Metamor-phic Geology, 1915.
Anatexis, Sederholm, 1907. --An ultrametamorphic
process in which deep-seated rocks are remelted
by the emanation of heat and hot gases from
below, thus providing regenerated magmas in
situ. Cf. Syntexis.
J. J. Sederholm : Bull. Comm. Geol. Finlande, 23, 1907,
Cong. Geol. Inter. C.R. xii (1913), 1914, p. 319.
P. J. Holmquist : Bull. Geol. Inst. Upsala, 15, 1916, p. 141.
Anchi-etttectic, Vogt, 1905. A term applied to those
rocks which are composed almost wholly of two or
more minerals in nearly eutectic proportions.
J. H. L. Vogt : References as below.
Anchi-monomineralic, Vogt, 1905. A term applied
to those rocks which are composed almost wholly
of one kind of mineral; e.g., anorthosite, bron-
zitite, congressite, dunite, etc.
J. H. L. Vogt: Norsk Geol. Tidsskrijt, i, No. 2, 1905:
Vidensk. Selsk. Skrift. Math- nat Klasse, No. 10, 1908.
Anchorite, Lapworth, 1898. A nodular and veined
variety of diorite, the normal fades of the rock
being variegated with dark mafic segregation
patches and light felsic contemporaneous veins.
(Anchor Inn, near Caldecote, Nuneaton.)
C. Lapworth : Proc. Geol. Assoc., xv, 1898, p. 419.
Anden-diorite, Stelzner, 1885. A variety of quartz-
iferous diorite having augite as its principal mafic
mineral. (Argentine Andes.)
Andesinite, Turner, 1900. -- A phanerocrystalline
rock composed almost entirely of andesine.
Andesite, Von Buck, 1826.- A volcanic rock, gener-
ally porphyritic, composed essentially of plagioclase
32 THE NOMENCLATURE OF PETROLOGY
(andesine or oligoclase, or having an average com-
position corresponding to those types), together
with one or more of the mafic minerals, biotite,
hornblende, and pyroxenes. The modern primary
distinction between andesite and basalt does not
depend on the absence or presence of olivine, or
on the relative proportions of felsic to mafic
minerals (though each of these criteria have been
applied in the past), but on the composition of
the plagioclase. (Andes.)
J. J. H. Teall : Geol. Mag., 1883. pp. 100, 145, 252, 344.
J. P. Iddings : Journ. Geol., i, 1893, p. 166.
J. W. Sollas : Rocks of Cafe Colville Peninsula, New Zea-
Mem. Geol. 9 Surv. Scot. 53 (Ben Nevis and Glen Coe), rgi6,
. An achondritic meteoritic stoiie consisting
mainly of purple titaniferous augite (over 90 per
. cent.) and olivine.
Anhedral, Pirsson, 1895. See Allotriomorphic.
Anhedron, Pirsson, 1895. A term applied to crystals
which have failed to develop the faces naturally
suggested by the term crystal.
L. V. Pirsson : Bull. Geol. Soc. Am., vii. 1895, 492.
Ankaramite, Lacroix, 1916. A melanocratic basaltic
rock, poor in plagioclase and richer in augite than
in o\i\me=felspathic augitite.
A. Lacroix : C.R., clxiii, 1916, p. 182.
Ankaratrite, Lacroix, 1916. -- Melanocratic forms of
nepheline-basalt with phenocrysts of olivine ; some
varieties contain melilite.
(Mt. Ankaratra, Madagascar.)
A. Lacroix : C.R., clxiii, 1916, p. 256.
Anorthite-basalt, Wada, 1882. A variety of basalt,
containing anorthite (An 90 -An 100 ) as the essential
felspathic mineral. (Fuji Yama, Japan.)
Anorthite Rock, Irving, 1883. -- A variety of anor-
thosite, consisting mainly of anorthite.
(L. Superior, Minnesota.)
R. D. Irving : U.S.G.S., Man. v, 1883, p. 59.
THE NOMENCLATURE OF PETROLOGY 33
Anorthosite, Sterry Hunt, 1863. -- A leuoocratic
gabbro or norite, nearly free from pyroxene, and
thus composed essentially of a plagioclase (Fr.
= anorthose), which is usually not less calcic than
N. L. Bowen : Journ. GeoL, xxv, 1917, p. 209.
Anthracite. A variety of coal, containing- less than
10 per cent, of volatile matter and over 90 per
cent, of carbon, and which therefore burns slowly
with a smokeless flame. Anthracite can be
handled without soiling the fingers and has a high
A. Strahan : Mem. Geol. Surv. (Coals, S. Wales), 1915,
Anthraconite. A term applied to black bituminous
limestones or marbles.
Anthraxolite. - - A coal-like and lustrous variety of
bitumen; 11=3 4; S.G.= nearly 2. The same
term has also been used to describe bituminous
and anthracitic matter occurring as enclosures in
Anti-Stress Minerals, Barker, 1918. A term sug-
gested for minerals such! as anorthite, potash-
felspars, pyroxenes, forsterite, andalusite, etc.,
whose formation in metamorphosed rocks is fav-
oured by conditions controlled, not by shear-
ing stress, but by thermal action and hydrostatic
pressure ; contrasted with stress-minerals (q.v.).
A. Harker : Q.J.G.S., Ixxiv, 1918, p. Ixxviii.
Apachite, Osann, 1896. A variety of nepheline-phoncv
lite, rich in alkali-pyroxenes and amphiboles.
(Apache Mts., Texas.)
Aphanite, Haiiy, 1822. A term first applied to com-
pact rocks of dioritic composition ; now extended
to any fine-grained igneous rock or groundmass
(said to be aphanitic), the constituents of which
cannot be distinguished by the unaided eye.
Aphrolith, Jaggar, 1917. A term, meaning "foam-
stone, ' ' applied to block-lava or aa-lava.
T. A. Jaggar : Jour. Wash. Acad. Sci., vii, 1917.
34 THE NOMENCLATURE OF PETROLOGY
Aplite, Retz. -- A leucocratic microgranite occurring
as dykes or contemporaneous veins ; muscovite
may be present. Sometimes written Haplite.
Aplodiorite, Bailey, 1916. A leucocratic variety of
biotite-granodiorite containing little or no horn-
E. B. Bailey : Mem. Geol. Surv. Scotland, 53 (Ben Nevis &
Glen Coe), 1916, pp. 160, 166.
Aplogranite, Bailey^ 1916. -- A term for leucocratic
rocks of granitic texture consisting essentially of
alkali-felspar and quartz, with subordinate biotite ;
muscovite may be present or absent.
E. B. Bailey : Mem. Geol. Surv. Scotland, 53 (Ben Nevis &
Glen Coe), 1916, p. 158.
ApO-. A prefix implying the derivation of one kind of
rock from another ; applied specifically to the
names, of volcanic rocks to indicate that they have
suffered devitrification, e.g., aporhyolite. Van
Hise proposed aposandstone for quartzite, apogrit
for grauwacke, and other analogous terms.
F. Bascom : Journ. Geol., i, 1893, p. 828.
C. R. Van Hise : U.S.G.S. Mon. 47, 1904, p. 776.
Apophyses. - - Veins, tongues, or dykes that can be
directly traced to larger intrusions, from which
they are offshoots.
Appinite, Bailey, 1916. -- A group term for melano-
cratic varieties of syenite, monzonite or diorite,
which are rich in hornblende ; like the vogesites
and spessartites, of which appinite is regarded as
the " plutonic " equivalent, secondary minerals
are generally present. (Appin, Loch Linnhe.)
Mem. Geol. Surv. Scot., 53 (Ben Nevis and Glen Coe), 1916,
Aqueo-igncOUS. A term applied to minerals which are
of magmatic origin, and yet are not strictly pyro-
genetic because of their deposition from solutions,
which, though late-magmatic, are rich in water.
Amygdales and pegmatites afford examples.
Applied also to rocks formed of such minerals and
to the processes operative in their formation.
THE NOMENCLATURE OF PETROLOGY 35
Arapahite, Washington &> Larsen, 1913. A
melanocratic variety of basalt, containing about
50 per cent, of magnetite.
H. S. Washington & E. S. Larsen : Journ. Wash, Acad.
Sci., iii, 1913, p. 449.
Arctic Suite, ^. Wolff, 1914. A general term for the
basaltic and associated rocks of the Brito-Arctic
province, drawing attention to the fact that they
do not clearly belong to either the Atlantic or the
Pacific suite, but occupy a petrographic position of
an intermediate character corresponding with their
geographical situation between the alkali-rocks of
the Atlantic Islands and the andesitic-rocks of the
F. v. Wolff : Der Vulkanismus, Bd. I (2), 1914, p. 427.
A. Holmes : Min. Mag., xviii, 1918, p. 180.
Arenaceous = Psammitic. -- Terms applied to sedi-
mentary rocks composed of grains of sand, loose
Argillaceous = PelitlC. Terms applied to sedimentary
rocks characterised by an abundance of clay
minerals, and a predominance of the " mud "
W. M. Hutchings : Geol. Mag., 1890, pp. 264, 316: 1891, p.
164; 1892, pp. 154, 218; 1894, pp. 36, 64; 1896, pp.
Argillite. An argillaceous rock cemented by silica,
and therefore more compact and less clearly
laminated than shale.
Ariegite, Lacroix, 1901. A type of pyroxenite rich in
alumina, containing variable amounts of spinel,
pyrope, and sometimes of hornblende.
A. Lacroix : Cong. Geol. Inter., C.R. viii (Paris, 1900), 1901,
Arizonite, Spurr & Washington, 1917. A dyke
rock, containing 80 per cent, of quartz and 18 per
cent, of orthoclase. (Arizona.)
36 THE NOMENCLATURE OF PETROLOGY
Arkite, Washington, 1901. - - A holocrystalline por-
phyritic rock), composed of leucite (or pseudo-
leucite), nepheline, cegirine-augite and melanite.
(Magnet Cove, Arkansas.)
H. S. Washington : Jonrn. GeoL, ix, 1901, p. 615.
Arkose, Brongniart, 1823. A coarse-grained richly-
felspathic sandstone or grit, derived from the rapid
disintegration of granite or gneiss. Arkose thus
differs from felspathic grit and sandstone by con-
taining a high percentage of felspar which has
suffered little, if any, alteration by weathering.
D. C. Barton : Journ. Geol., xxiv, 1916, p. 417.
Arso Trachyte. A type of olivine-trachyandesite con-
taining phenocrysts of sanidine, oligoclase, augite
and olivine in a trachytic groundmass containing
interstitial glass. The type is thus related to
rhomb-porphyry and kenyte.
(Lava of 1302, Ischia.)
Articulite, Wether ell, 1867. = Flexible Sandstone.
Aschaffite, G umbel, 1865. A lamprophyric dyke-rock
containing quartz and plagioclase, with abundant
biotite among the femic minerals.
Aschistic, Brogger, 1894. A term applied to those
rocks of minor intrusions which have not suffered
differentiation into leucocratic and melanocratic
modifications, but which have nearly the same
composition as the larger intrusions with which
they are associated.
Ash, Volcanic. Fine-grained pyroclastic material
composed of comminuted glass, crystals, and/or
cryptocrystalline or micro-crystalline rock sub-
stance. The term is, however, becoming obsolete,
partly because of its ordinary connotation, and
partly because in British literature it has not been
confined to fine-grained material, but has been
used synonymously with Tuff.
THE NOMENCLATURE OF PETROLOGY 37
Asphalt. A black, glossy, and brittle variety of
G. H. Eldridge : U.S.G.S. 22nd Ann. Re-p., Ft. i, 1901, p.
H. Kohler : Die Chemie und Technologie der Natiirlichen
und Kiinstlichen Asphalte, 1913.
H. Abraham : As-phalts and Allied Substances, 1918.
Asphaltite. -- A group-term sometimes used for the
solid forms of the purer bitumens, such as albe,r-
tite, grahamite, and uintaite, to distinguish them
from bituminous sands and limestones, which com-
mercially are often described as " asphalt."
Assimilation, Michel-Levy, 1893. - The process
whereby material from the containing walls of an
intrusion is absorbed by solution in the invading
magma, either in situ (or nearly so) at the con-
tacts, or in depth, ,by the sinking through the
magma of blocks or fragments stoped from the
W. J. Miller : Bull. Geol. Soc. Am., xxv, 1914, p. 243.
R. A. Daly : Igneous Rocks and their Origin, 1914.
Journ. Geol., xxvi, 1918, p. 126.
Assyntite, Shand, 1909. A variety of augite-bearing
sodalite-syenite. (Assynt, N.W. Highlands.)
S. J. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 403.
Asthenosphere, Barrell, 1914. -- A thick zone lying
beneath the more rigid lithospherej in which
plasticity reaches a maximum, in which isostatic
and other readjustments are effected, and in which
magmas may be generated.
J. Barrell : Journ. Geol., xxii, 1914, p. 680; and xxiii, 1915,
A. Holmes : Geol. Mag., 1916, p. 267.
J. Barrell : Am. Journ. Sci., xlviii, 1919, pp. 281, 291.
Astite, Salomon, 1898. - - A variety of hornfels, in
which mica and andalusite are the dominant
minerals. (Cima d'Asta, Italian Alps.)
Atatschite, Morozeinicz, 1901. -- A variety of hyalo-
orthophyre, characterised by the presence of small
amounts of sillimanite, and locally of cordierite.
38 THE NOMENCLATURE OF PETROLOGY
Orthoclase, augite and biotite occur as micro-
scopic crystals in a glassy base.
(Atatsch Mt., Southern Urals.)
J. Morozewicz : Mem. Comm. Geol. Russia, xviii (i), 1901,
Ataxic, Keyes, 1901. A general term applied to un-
stratified ore-deposits, as opposed to those that are
stratified, or eutaxic.
C. R. Keyes : Trans. Amer. Inst. Min. Eng.< xxx, 1901,
P- 3 2 3-
Ataxite, Loewinson-Lessing, 1888. -- A brecciated or
irregularly mottled composite! volcanic rock, in
which the broken fragments of one lava-flow are
irregularly distributed in another. A similar
structure to which the term may also be applied
occurs in certain minor intrusions.
Ataxite, Brezina, 1896. A general term for siderites
(iron-meteorites) which contain less nickel than
hexahedrites or more than octahedrites, and so fail
to exhibit the structures characteristic of those
Atlantic Suite, Harker, 1896. A general term for the
whole assemblage of alkali-rocks, directing atten-
tion to their distribution in and around the
Atlantic, to their association with the Atlantic type
of coast-line, and more generally to their associa-
tion with tectonic structures due to tension, frac-
ture and differential radial movements. Cf.
Pacific Suite. See Alkali-rocks.
G. T. Prior : Min. Mag., xiii, 1903, p. 228.
A. Harker : Nat. Hist. 1 g. Rocks, 1909, p. 90.
J. S. Flett : Geol. Mag., 1912, p. 517.
J. W. Gregory: Scientia, xi, 1912, p. 56.
A. Holmes: Geol. Mag., 1916, p. 272; Geol. Map., xviii,
1918, p. 220.
Aubrite, Prior, 1919. -- A group name for enstatite
achondrites, including Aubres, Bishopville and
Bustee. Cf. Chladnite.
THE NOMENCLATURE OF PETROLOGY 39
Auganite, Winchett, 1912. - - A term suggested for
augite-andesite to avoid the use of a compound
A. N. Winchell : Jonrn. GeoL, xxi, 1913, p. 215.
Augen-gneiss. A general term for gneissose rocks,
independently of their origin, containing " eyes,"
i.e., phacoidal or lenticular crystals, or aggre-
gates, which simulate the porphyritic crystals of
igneous rocks. The "eyes" may be porphyro-
blastic or blasto-porphyritic crystals, or, in the case
of composite gneisses, porphyritic crystals belong-
ing to the injected component of the rock.
Augen-SChist, Lapworth, 1885. -- A rock associated
with mylonite, and composed of granulated
minerals, aggregates of which occur as " augen,"
surrounded by and alternating with schistose
streaks and lenticles of completely recrystallised
minerals. In mylonite the rolling out has been
effected with but little recrystallisation. Cf.
C. Lapworth : Nature, 1885, p. 559.
Augitite, Doelter, 1882. A volcanic rock, containing
phenocrysts of augite and iron-ore, with or with-
out biotite or hornblende, in a base of brown glass,
which is usually a soda-rich variety. = Magma
basalt (in part).
Aureole. -- A term applied to the zone of contact-
metamorphosed rocks surrounding an intrusion.
Australite. A term used to distinguish the obsidian-
ites of Australia from those of Bohemia (Molda-
vites) and Billiton (Billitonites). Cf. Obsidianite.
H. S. Summers : Aust. Ass. Ad. Set. (Melbourne, 1913), xiv,
1914, p. 189.
C. G. Thorpe : Nat. Hist, and Sci. Soc. W . Australia, 1914,
E. W. Skeats : Proc. Roy. Soc. Victoria, xxvii, 1915, p. 362.
Authigenous, or Authigenic, Kalkovsky, 1880.
Terms, meaning generated on the spot, applied to
those constituents that came into existence with
or after the formation of the rock of which they
40 THE NOMENCLATURE OF PETROLOGY
constitute a part; e.g. , the primary and secondary
minerals of igneous rocks, and the cements of
sedimentary rocks. Cf. Attothigenous.
Autochthonous, Giimbel, 1888. -- A term applied to
rocks such as rock-salt and stalactite, denoting
that they and their constituents have been formed
in situ. Cf. Allochthonous.
Autodastic, Van Plise, 1894. A term applied to rocks
that have been brecciated in place by mechanical
processes, e.g. , crush breccias.
Autolith, Holland. A fragment of igneous rock en-
closed in another igneous rock of later consolida-
tion, each being- regarded as a derivative from a
common parent magma. = Cognate Inclusion.
T. H. Holland : Mem. Geol. Siirv. India, xxviii, iqoo. p. 217.
Autometamorphjsm, Sargent, 1917. The metamor-
phism of an igneous rock by the action of its own
volatile fluxes; e.g. , the' formation of spilite from
basalt. Cf. Autopneumatolysis.
H. C. Sargent : Q.J.G.S., Ixxiii, 1917-18, p. 19.
Automorphic, Rohrbach, 1886. - - See Idiomorphic.
Autopneumatolysis, Lacroix, 1907. The production
of new minerals in an igneous rock by the action
of its own mineralising agents; e.g., the forma-
tion of sanidine, sodalite, biotite, etc., in the
leucite-tephrites of Vesuvius.
A. Lacroix : Nouv. Arch, du Mus. d^Hist. Nat., ix, 1907,
Avezacite, Lacroix, 1901. A phanerocry stall ine dyke
rock, composed of augite and hornblende, with
titaniferous iron-ore, apatite, and sphene as
abundant accessories. The type-rock is cata-
clastic in structure. (Avezac, Pvrenees.)
A. Lacroix : Cong. Geol. Inter., C.R., viii (1900), 1901, p.
Aviolite, Salomon, 1898. A variety of hornfels, con-
sisting essentially of mica and cordierite.
(Monte Aviolo, Italian Alps.)
THE NOMENCLATURE OE PETROLOGY 41
AxiolitlC, Zirkel, 1876. -- A term applied to a com-
posite spherulitic texture, in which the spherulitic
bodies are elongated along- a central axis, to
which the radiaiting fibres are normal.
Bahiaite, Washington, 1914. A variety of hypersthe-
nite, containing- abundant hornblende with smaller
amounts of olivine and pleonaste.
H. S. Washington : Am. Journ. Sci., xxxviii, 1914, p. 86.
Ballstone. A Shropshire term for an irregular len-
ticular mass of unstratified limestone occurring- in
the Wenlock and other Palaeozoic limestones.
Examples vary in dimensions up to 60 feet or
more, and are found to consist of colonies of corals
and stromatoporoids (in the position of growth)
enveloped in a matrix of calcareous mud.
M. C. Crossfield & M. S. Johnston : Proc. Geol. Assoc.< xxv,
1914, p. 193.
Banakite, Iddings, 1895. A variety of trachydolerite
similar mineralogically to absarokite but contain-
ing less olivine and augite, and in some varieties
being free from olivine, or even containing quartz.
J. P. Iddings : Joiirri. Geol., iii, 1895, p. 947.
Banatite, v. Cotta. An orthoclase-bearing variety of
Bandaite, Iddings, 1913. A general term for " lab-
radorite-dacites " ; i.e., for quartz-basalts which in
texture resemble dacites or andesites.
(Bandai San, Japan.)
Banded Structure- A structure developed in many
igneous and metamorphic rocks, due to the alter-
nation of layers which differ conspicuously in
mineral composition or texture, or both.
F. F. Grout : Journ. Geol., xxvi, 1918, p. 439.
42 THE NOMENCLATURE OF PETROLOGY
Banket. A term of Dutch origin originally applied to
the auriferous Witwatersrand conglomerates, and
now used more widely for other compact siliceous
vein-quartz conglomerates, which have pebbles of
about the size of a pigeon's egg, and in general
possess the megascopic characters of the type-rock
from the Rand.
R. B. Young :JThe Banket , London, 1917.
W. H. Goodchild : Mining Mag., xix, 1918, p. 194.
Barolite, Wadsworth, 1891. -- A term suggested for
rocks composed of barytes or celestine.
Basalt. A microlithic or porphyritic igneous rock of
a lava flow or minor intrusion, often vesicular or
amygd'aloidal, having an aphanitic texture as a
whole or in the groundmass, and composed essen-
tially of plagioclase (at least as calcic as labra-
dorite), and pyroxene, with or without interstitial
glass. When olivine is present the rock is termed
an olivine-basalt. In the field the term basalt is
generally applied only to lava flows, the corre-
sponding rocks of minor intrusions being called
dolerite. The original distinction between basalt
and dolerite was based simply on degree of granu-
larity, basalt being a compact rock, while dolerite
was recognisably crystalline, i.e., the component
minerals were sufficiently large to reflect light in-
dividually, even though they were too small for
A. Harker : Mem. Geol. Surv. Scot. (Tert. Ig. Rocks Skye),
1904, p. 29.
H. S. Washington : Q.J.G.S., Ixiii, 1907, p. 69 (Mediter-
Mem. Geol. Surv. Scot. (Glasgow District), 1911, p. 135.
G. W. Tyrrell : Trans. Geol. Soc. Glas., xiv, 1912, p. 210
W. Cross : U.S.G.S., Prof. Pap., 88, 1915 (Hawaii).
A. Holmes : Q.J.G.S., Ixxii, 1916, p. 260 (E. Africa).
O. Backstrom : Bull. Geol. Inst. Univ. U-psala, xiii, 1916,
p. 115 (Antarctica).
A. Holnies : Min. Mag., xviii, 1918, p. 180 (Arctic).
THE NOMENCLATURE OF PETROLOGY 43
Basal tite. An old term revived by the International
Congress in 1900, and adopted to denote basalts
Basanite, Brongniart, 1813. A basaltic rock, gener-
ally porphyritic, containing plagioelase, augite,
olivine, and a felspathoid ; nepheline-, leucite-, and
analcite-basanites are distinguished. In the
original usage of the term, olivine was not neces-
sarily an essential component. The type is now,
however, distinguished from tephrite by the pre-
sence of olivme.
Basanitoid, Bucking, 1881. A term used for alkali-
basalts free from nepheline, but containing a soda-
rich iso tropic base. By Lacroix it has been more
recently denned as a basaltic rock having the
chemical composition of basanite, but free from
A. Lacroix : C.R., clxix, 1919, p. 402.
Basic. A term applied to igneous rocks having a re-
latively low percentage of silica, the limit below
which they are regarded as basic being about 52
per cent. Cf. subsilicic and under saturated.
Basis. See Mesostasis.
Batholith, Suess, 1888. A large transgressive intru-
sion with sides generally steeply inclined, and with
no visible or de terminable floor. Smaller intru-
sions of similar relations are variously called
Stocks, Bosses, or Domes.
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 89.
Batukite, Iddings & Morley, 1917. A porphyritic vol-
canic rock containing phenocrysts of augite and
fewer of olivine, in a groundmass of augite, mag-
netite, and leucite. The rock is thus a melano-
cratic leucite-basalt. (Batuku, Celebes.)
J. P. Iddingp & E. W. Morley : Proc. Nat. Acad. Sci. f iii,
'Q 1 ?! P- 595-
Bauxite, Dufrenoy, ^847. - - An amorphous mineral
having the composition represented by
A1 2 O 3 .2H 2 O. The name is also applied com-
44 THE NOMENCLATURE OF PETROLOGY
mercially to aluminous lateritic rocks in which
aluminium hydroxides, amorphous or crystalline,
predominate over other lateritic constituents.
Further confusion has been introduced by pro-
posals (a) to use bauxitite (DHtler and Doelter,
1912) for a rock mainly composed of bauxite, and
(b) to use bauxitite (Campbell,.!*:)!?) for the mineral
bauxite as denned above. The latter usage is
clearly inadmissible, and the former serves little
purpose, as most of the rocks referred to as
bauxite contain very little of the mineral properly
so called, though many of them correspond to it
in their bulk chemical composition on account of
the presence of both A1 2 O 3 .H 2 O and A1 2 O 3 .3H 2 O.
W. J. Mead : Econ. GeoL, x, 1915, p. 28.
T. L. Watson : Geol. Sttrv. Georgia, Bull, n, 1916.
J. Morrow Campbell : Mining Mag., 1917, p. 171.
Bean Ore. A loose pisolitic iron ore of Tertiary age ;
distinguished from mine'tte by the larger size of the
Becke Method. A microscopic method of determin-
ing which of two materials in contact has the
higher or lower average refractive index. The
amount of illumination is reduced and the focus
adjusted until the contact between a mineral with
liquid, Canada balsam, or another mineral appears
as a relatively bright line. On raising the objec-
tive a band of illumination moves into the material
having the higher refractive index ; while on lower-
ing the objective the band moves into the substance
with the lower index.
Beerbachite, Chelius, 1894. A fine-grained gabbro,
often leucocratic, occurring in aplite-like veins or
dykes ; composed essentially of labradorite and
diallage, with hypersthene and magnetite.
Bekinkinite, Rosenbusch, 1907. A melanocratic rock
containing titanaugite with nepheline and a little
felspar as essential minerals. Soda-amphibole,
biotite and analcite are often present and most ex-
Samuel S. Clark
THE NOMENCLATURE OF PETROLOGY 45
amples are olivine-bearing. By Lacroix bekin-
kinile is regarded as a variety of theralite in which
the dominant white mineral is analcite.
G. W. Tyrrell : Geol. Mag., 1915, pp. 304 and 361.
A. Lacroix : C.R., clxx, 1920, p. 20.
Belonite, Vogelsang, 1872. A needle-shaped crystal-
lite with pointed or rounded ends.
Belugite, Spurr, 1900. A term applied to rocks inter-
mediate (in respect of their felspar) between dior-
ite and gabbro; i.e., containing andesine and/or
labradorite. (Beluga River, Alaska.)
J. E. JSpurr : Amer. Geol.) xxv, 1900, p. 233.
Bentonite. A white clay-like rock largely composed
of colloidal silica and characterised by its capacity
for absorbing large quantities of water.
(Rosedale Mine, Alberta.)
Beresite, Rose, 1840. A quartz-rich variety of aplite,
often characterised by the presence of pyrite.
J. E. Spurr : Am. Journ. Sci., x, 1900, p. 358; U.S.G.S. zoth
Ann. Re-p., Ft. vii, 1900, p. 195.
Bergalite, Soellner, 1913. - - A black pitch-like dyke
rock containing small phenocrysts of haiiyne,
apatite, perovskite, melilite, and magnetite, in a
groundmass of the same minerals with nepheline
and biotite and brown interstitial glass
Beringite, Hafsinskij 1912. A melanocratic variety
of soda-trachyte rich in barkevikite.
(Bering Is., Kamchatka.)
Bermudite, Pirsson, 1914. A lamprophyric volcanic
rock containing abundant small biotite crystals,
with accessory iron-ores and apatite, in an obscure
analcitic base. The type is thus the effusive
equivalent of biotite-monchiquite or ouachitite. In
some varieties augite (brown to colourless) is also
present. (Bermuda Is.)
V V. PirssoL. : Am. Journ. Sci.> xxxviii, 1914. p. 340.
40 THE NOMENCLATURE OF PETROLOGY
Berondrite, Lacroix, 1920. A type of theralite char-
acterised by the presence of elongated crystals of
brown hornblende associated with titaniferous
augite. Cf. Luscladite.
(R. Berondra, Madagascar.)
A. Lacroix : C.R., clxx, 1920, p. 22.
Beschtauite, Gerassimow, 1910. A soda-rich variety
of quartz-porphyry ; = quartz-keratophyre.
(Mt. Beschtau, Caucasia.)
Billitonite, F. Suess, 1900. A general term for the
obsidianites of the Malay Peninsula and Archi-
Binary Granite, Keyes y 1895. A term applied origin-
ally to granites containing only the essential
minerals quartz and felspar, but now used to con-
note granites which contain both the common
micas, muscovite and biotite.
BirdVEye Slate. - - A quarry man's term for slate
crowded with squeezed concretions. The term
Bird's-eye is given in Guernsey to a variety of
Birkremite, Kolderup, 1903. -- A leucocratic quartz-
syenite containing alkali-felspars, together with
small amounts of quartz and hypersthene.
F. Loewinson-Lessing : Verh. Russ. Min. Ges. St. Pet., xlii,
1905, p. 262.
Bitumen. A group name for natural substances com-
posed of hydrocarbons, ranging in types from
petroleum (mobile), through mineral tars (viscous),
to asphalt (rigid).
G. H. Eldridge : U.S.G.S. 22nd Ann. Re-p., Pt. i, 1901, p.
H. Kohler : Die Chemie und Technolgie der Naliir lichen
und Kiinstlichen As-phalte, 1913.
Black-band Ironstone. A variety of clay ironstone
containing sufficient carbonaceous matter to allow
of calcining without the addition of fuel in a separ-
THE NOMENCLATURE OF PETROLOGY 47
Blaes. A Scottish name for carbonaceous shales of a
grey-blue colour, associated in the Lothians with
oil-shales. They differ from the latter in having 1 a
low content of bituminous matter, in being- brittle
rather than tough, and in weathering- to a crumb-
ling- mass which passes into soft clay.
Mem. Geol. Surv. Scotland (Oil Shales, Lothians), iQi2>
Blairmorite, MacKenzie, 1919. A porphyritic volcanic
rock characterised by an abundance of analcite
phenocrysts, in a groundmass of analcite, alkali-
felspar and alkali-pyroxenes.
(Blairmore, Crowsnest Pass, Alberta.)
Geol. Surv. Canada, Museum Butt. No. 4, 1914, p. 19.
Blast. A syllable indicating the process of recrystal-
lisation in a highly viscous mass during- the meta-
morphism of rocks. It is used as a suffix in terms
like idioblast and porphyroblast to indicate the
form or relations of individual crystals. The
termination -blastic is used in words like grano-
blastic and poikiloblastic to denote the textures of
the rocks produced. As a prefix, blasto-, it appears
in terms like blastophitic and blastoporphyritic to
connote a relict texture veiled, but not entirely
destroyed by recrystallisation.
U. Grubenmann : Die Kristattinen Schiefer, i, 1904.
Blasto-porphyritic, Becke, 1903. A term applied to
the textures of metamorphic rocks derived from
porphyritic rocks, and in which the porphyritic
character still remains as a relict feature, veiled
but not obliterated by subsequent recrystallisation.
Block-lava. A term applied to lava flows which occur
as a tumultuous assemblag-e of angular blocks
having extremely rough surfaces due to the abun-
dant development of large vesicles; = aa-lava or
Blue Ground. A term applied to the slaty-blue or blue-
green kimberlite-breccia of diamond pipes, occur-
4 THE NOMENCLATURE OF PETROLOGY
ring" beneath a superficial oxidised covering known
as Yellow Ground. (Kimberley.)
P. A. Wagner : The Diamond Fields of South Africa, 1914
Blue Mud.- A common variety of deep-sea mud hav-
ing- a bluish-grey colour due to the presence of or-
ganic matter and finelv-divided iron-sulphides ;
CaCO 3 present in variable amounts up to 35
J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea
Deposits), 1891, p. 229.
Bogen Structure, Milgge. A term for the structure
of vitric tuffs composed largely of shards and
" bows " of glass, formed by the explosive vesicu-
lation of lavas, or by the breaking of pumice or
other highly vesicular vitreous rocks.
Bog Iron Ore. A g-eneral term for impure ferruginous
deposits formed in bogs or swamps by the oxidis-
ing action of al"ae, bacteria, or the atmosphere.
In the presence of decavingf vegetation, which acts
as a reducine aeent, siderite is deposited.
E. C. Harder : U.S.G.S., Prof. Pap. 113, 1919.
Bojite, Weinschenk. - - A term suggested for horn-
blende-gabbros in general. The type rock con-
tains augite and biotite in addition to hornblende.
Bole. A bright-red, waxy or unctuous decomposition
product of basaltic rocks, having the variable com-
position of lateritic clays.
Mem. Geol. Surv. Ireland (Interbasaltic Rocks), 1912, p. 18.'
Bombs. Ellipsoidal, discoidal, or irregularly rounded
masses of lava ejected at a high temperature dur-
ing a volcanic eruption. Bombs vary in size from
that of the largest lapilli upwards. They are char-
acterised by a well-defined crust, and are often
cellular or even hollow, internally.
Boninite, Peter sen, 1891. A hyalo-andesite with occa-
sional phenocrysts of andesine and hypersthene.
(Bonin Is., Japan.)
THE NOMENCLATURE OF PETROLOGY 49
Borolanite, Teall, 1892. A phanerocrystalline igneous
rock composed essentially of orthoclase and mela-
nite with subordinate nepheline, biotite, and pyrox-
ene. Orthoclase and nepheline (or sodalite)
sometimes form rounded pseudo-porphyritic masses
resembling- leucite. (L. Borolan, Assynt.)
S. J. Shand : Trans. Edin. Geol, Soc., ix, 1909, p. 202, and
1910, p. 376.
BOSS. A transgressive intrusion of igneous rockjike
a stock or dome. The term is also applied to
forms of less regular outline than the latter, and is
therefore of wider application.
Bostonite, Rosenbusch, 1882. A leucocratic alkali-
syenite-aplite with trachytic texture ; formed almost
wholly of alkali-felspars. (Boston, Mass.)
Boulder Clay. - - A tenacious unstratified deposit of
glacial origin consisting of a stiff clay (rock flour)
packed with subangular stones of varied sizes.
Bowenite. A translucent variety of serpentine com-
posed of a dense felt-like aggregate of colourless
serpentine-fibres, with occasional patches of mag-
nesite, flakes of talc, and grains of chromite. The
rock occurs as veins in a foliated rock containing
the same minerals, but with talc as the dominant
constituent. (New Zealand.)
A. M. Finlayson : Q.J.G.S., Ixv, 1909, p. 361.
Bowralite, Ma-wson, 1906. A pegmatoid rock consist-
ing of idiomorphic sanidine with subordinate soda-
amphibole (arfvedsonite) and agirine.
(Bowral, N.S. Wales.)
D. Mawson : Proc. Linn. Soc. N.S.W., xxxi, 1906, p. 606.
Box-Stones. -- A local (Suffolk) name for masses of
brown ferruginous or phosphatic sandstone,
rounded or flattened in form, and in size generally
a little larger than that of the closed fist. Some
specimens are more concretionary than others,
and, on being broken, are found to enclose fossil
remains : hence the name.
P. G. H. Boswell : Geol. Mag., 1915, p. 250.
50 THE NOMENCLATURE OF PETROLOGY
Braccianite, Lacroix, 1917. - - A variety of leucite-
tephrite, having- the chemical composition of cer-
tain leucitites. (Bracciano, Italy.)
A. Lacroix : C.R., clxv, 1917, p. 1030.
Breccia. A clastic rock made of coarse angular or sub-
angular fragments of varied or uniform composi-
tion, and of either exogenetic (e.g., scree or mo-
raine breccias) or endogenetic origin (e.g., volcanic
T. G. Bonney : Q.J.G.S., Iviii, 1902, p. 185.
W. H. Norton : Journ. Geol., xxv, 1917, p. 160.
Bronzitite, Lacroix, 1894. A rock composed wholly
or almost wholly of bronzite.
A. Lacroix : Nouv. Arch. Mus. d'Hist. Nat., vi, 1894, p. 304.
Brotocrystal, Lane, 1902. A term applied to crystals
having corroded or embaved outlines.
A. C. Lane : Bull. Geol. Soc. Am., xiv, 1902, p. 386.
Brown Cpal, see Lignite. Brown coal is now distin-
guished chemically from bituminous coal by con-
taining more than 10 per cent, of water ; and from
lignite by containing less than 20 per cent.
Buchite. A vitrified rock produced from phyllite or
other material by intense local heat due to contact
with basalt magma, or to the thermal effects* of
friction in mylonised crush-belts.
J. S. Flett : Mem. Geol. Surv. Scot. (Oban), 1908, p. 129.
Buchnerite, Wadsworth, 1884. A term for peridotites
containing both monoclinic and ortho-rhombic
pyroxenes. The term has not been adopted, as
Lherzolite has priority.
Buchonite, Sandberger, 1872. A variety of tephrite
^ containing hornblende and biotite in addition to
the usual minerals, plagioclase, nepheline, and
Buhr-Stone. A name given to certain varieties of
porous open-textured calcareous sandstones which,
on account of the angular character of the grains,
are suitable for millstones.
THE NOMENCLATURE OF PETROLOGY 51
BllStite, Tschermak, 1883. An achondritic meteorite
composed essentially of enstatite, with small
amounts of diopside and oligoclase, and a little
nickel-iron. Cf. Aubrite.
Bysmalith, Iddings, 1898. An injected intrusion
bounded by faults, and having- a roughly cylindri-
cal or plug-like form.
J. P. Tddings : Journ. Geol., vi, 1898, p. 704.
Calc-alkali Rocks. A term applied to igneous rocks
in which the proportions of lime and alkalies (in
relation to the other constituents) are such that the
dominant minerals are felspars, hornblende, and/
or augite, specifically alkali-minerals such as fel-
spathoids and soda-pyroxenes and amphiboles be-
ing absent. The term comprises such rocks as
granodiorite, syenite, diorite, and gabbrp, and their
volcanic analogues, and excludes alkali and spilitic
rocks, and most peridotites. The term is used
rather loosely to contrast rocks that are not " al-
kaline " with those that are, and cannot be strictly
limited by definition.
Calc-aphanite. A doleritic or diabasic rock which has
been largely replacecTby carbonate-minerals.
Calc-flinta, Barrow. A very fine-grained metamorphic
rock of flinty aspect derived from a calcareous
mudstone. The new minerals are in part due to
pneumatolytic processes, and include felspars and
calc-silicate-minerals, the latter being less abundant
than in calc-silicate-hornfels.
G. Barrow & H. H. Thomas : Min. Mag., xv, 1908, p. 113.
Mem. Geol. Surv., 347 (Bodmin and St. Austell), 1909, pp.
86 and 97.
Mem. Geol. Surv. 335-336 (Padstow and Camelford), 1910,
Calciphyre, Brongniart, 1813. A crystalline limestone
containing conspicuous calc-silicate minerals such
as forsterite, pyroxene, garnet, etc.
52 THE NOMENCLATURE OE PETROLOGY
Calcite-trachyte, Washington, 1917. - - A variety of
trachyte containing- over 10 per cent, of calcite,
probably primary. (Bilbao, Spain.)
Calcrete, Lamplugh, 1902. A term suggested for con-
glomerates formed by the cementation of superfi-
cial gravels by calcium carbonate. The term
Calcicrcte is suggested by Bonney as preferable.
G. W. Lamplugh : Geol. Mag., 1902, p. 575.
Mem. Geol. Surv. Ireland, 112 (Dublin), 1903, p. in.
Calc-SChist, Brongniart, 1827. A metamorphosed
argillaceous limestone in which calcite has recry-
stallised in elongated or platy forms, rather than
in the commoner granular forms, thus giving to
the rock with the other products of metamorphism
a schistose structure.
Calc-silicate-hornfels. An old term for contact-meta-
morphic rocks of variable but generally fine grain,
derived from marls and other calcareous sedi-
ments, and therefore containing a great variety of
minerals, mostly calc-silicates.
Caliche. A deposit occurring in the Chilian nitrate-
fields consisting of alluvium cemented with sodium
nitrate and chloride and other soluble salts. In
places, owing to recrystallisation, high-grade
saline layers nearly free from debris are associated
with the normal type of the deposit.
J. T. Singewald & B.' L. Miller: Econ. Geol., xi, 1916, p.
Campanite, Lacroix, 1912. A sodi-potassic variety of
leucite-tephrite sometimes containing large pheno-
crysts of leucite. (Mte. Somma.)
A. Lacroix : C.K., clxv, 1917, p. 1030.
Camptonite, Rosenbusch, 1887. A lamprophyre es-
sentially composed of plagioclase (generally labra-
dorite) and brown hornblende (generally barkevi-
kite). (Campton, New Hampshire.)
T. S. Flett : Trans. Roy. Soc. Edin., xxxix, 1900, p. 865.
V. Hackmann : Bull. Comm. Geol. Finlande, xlii, 1914.
THE NOMENCLATURE OE PETROLOGY 53
Canada-Balsam. A transparent and fluid oleo-resin
yielded by a North American species of silver fir ;
used for mounting microscopic preparations and
for cementing glass in optical instruments. Ex-
posed to the air, Canada-balsam becomes brittle
and discoloured, and its refractive index gradually
increases. The average values for refractive index
are 1.524 (uncooked), 1.538 (slightly undercooked),
and 1.543 (overcooked). In slides 30 years old
the value rarely exceeds 1.543; but for normally
cooked balsam the refractive index is between
1.534 and 1.540.
A. Johannsen : Journ. Geol., xx, 1912, p. 89.
Canadite, Quensel, 1913. A nepheline-syenite contain-
ing albite or an albite-rich plagioclase as the
principal felspar with abundant mafic minerals
which contain lime and alumina (i.e., normative
anorthite) ; the type is intermediate between albite-
nepheline-syenite and shonkinite.
(Almunge, Sweden, and Ontario, Canada.)
P. Quensel : Bull. Geol. Inst. U-psala, xii, 1913, p. 163.
Cancrinite-Syenite, Tornebohm, 1883. A variety of
felspathoid-svenite having cancrinite as the domi-
I. G. Sundell : Bull. Comm. Geol. Finlande, No. 16, 1905.
Canga. A Brazilian term for a ferruginous breccia ^or
conglomerate composed of fragments of haematite
and itabirite cemented together by limonite or
haematite, and occasionally by other lateritic con-
Cannel Coal. A dull lustreless variety of coal which
breaks with a conchoidal fracture. It is rich in
volatile combustibles, and burns with a bright
'Mem. Geol. Surv., Spec. Re<. Mineral Resoiirces of Great
Britain, vii. 1918.
Cantalite, Dujrenoy, 1845. - - A variety of rhyme-
A. Lacroix : C.R., 163, 1916, p. 47-
54 THE NOMENCLATURE OF PETROLOGY
Carmeloite, Laws on, 1893. A variety of augite-an-
desite or basalt (according as the plagioclase is
andesine or labradorite) characterised by the pre-
sence of iddingsite. (Carmelo Bay, California.)
A. C. Eawsoni : Bull. Dept. Geol. Univ. California, i, p.
CaSCadite, Pirsson, 1905. A lamprophyre ( = olivine-
augite-minette) with abundant phenocrysts of bio-
tite and fewer of olivine and augite in a ground-
mass principally composed of alkali-felspar.
(Highwood Mts., Montana.)
L. V. Pirsson: U.S.G.S., Bull. 237, 1905, p. 109.
Cataclastic, Kjerulf. A term applied to the structures
produced in a rock by the action of severe mecha-
nical stress during dynamic metamorphism, char-
acteristic features being the deformation and
granulation of the minerals. The term is also
applied to rocks characterised by such structures.
Cataclastic, Teall, 1887. A term applied to clastic
rocks, the fragments of which have been produced
by the fracture of pre-existing rocks by earth-
stresses; e.g., crush breccias.
Catapleiite-Syenite, Tornebohm, 19/36. A porphyritic
rock of tinguaite-habit containing phenocrysts of
catapleiite, and occasionally of eudialyte, in an
aphanitic but holocrystalline groundrriass com-
posed of those minerals with alkali-felspars,
nepheline, and aegirine.
(Korra Karr, Sweden.)
A. E. Tornebohm : Sveriges Geol. Under*., Ser. C., No. IQO,
Catawberite, Lieber. A metamorphic rock consisting
mainly of talc and magnetite. (S. Carolina.)
Catlinite. A red variety of siliceous clay occurring in
THE NOMENCLATURE OF PETROLOGY 55
Cauldron-subsidence. The sinking of part of the roof
of an intrusion within a closed system of peri-
pheral faults up which magmas have penetrated.
C. T. Clough, H. B. Maufe & E. B. Bailey : QJ.G.S., Ixv,
1909, p. 611.
E. B. Bailey : Geol. Mag., 1919, p. 466.
Cecilite, Cordier, 1868. A variety of leucitite charac-
terised by an abundance of melilite.
H. S. Washington : Carnegie Inst. Wash. Pub., 57, 1906,
Celyphitic, see Kelyphitic.
Cement. A term applied, as in mortar and concrete,
to the material binding together the allogenic frag-
ments or particles of clastic rocks. The term is
not used for the groundmass, matrix, or base of
igneous rocks. The process of cementation is the
filling of interstices in porous or shattered rocks.
Cenotypal, Brogger, 1894. A general term applied to
aphanitic and porphyritic igneous rocks having the
habit or suite of characteristics typical of fresh or
nearly-fresh volcanic rocks such as those of Recent
and Tertiary age. Crystals are lustrous, and
glass, where present, has not lost its brilliancy by
devitrification ; whereas in the older rocks felspars
and glass have become dull and lustreless by
decomposition and devitrification. Rocks having
the older-looking, dense and compact habit are
described as paleotypal. The two terms constitute
an attempt to express the essential differences
between the two groups of aphanitic rocks vari-
ously distinguished as Tertiary and pre-Tertiary,
fresh and altered, hypabyssal and volcanic : differ-
ences that are recognised in the nomenclature of
rocks by two groups of terms such as rhyolite and
quartz-porphyry, andesite and porphyrite, basalt
Centric, Becke, 1878. A textural term applied to the
arrangement of crystalline matter in regular
56 THE NOMENCLATURE OF PETROLOGY
groups around or about a centre, as in spherulites,
variolites, oolites, etc.
Ceratophyre, see Keratophyre.
Chadacrysts, Iddings, 1909. The relatively small
crystals scattered as poikilitic inclusions through a
host crystal (oikocryst) of another mineral.
Chalk. A fine-grained somewhat friable foraminiferal
limestone of Cretaceous age occurring in Britain,
north-western Europe and elsewhere.
Mem. Geol. Surv. (Cretaceous Rocks of Britain), Vol. 2, 1903,
p. 499; Vol. 3, 1904, p. 302.
Charnockite, Holland, 1893. -- A granular variety of
hypersthene-granite, composed of hypersthene,
microcline-perthite, quartz and iron-ores. " Named
after Job Charnock, the founder of Calcutta, whose
tombstone (1695) was the first specimen of the rock
T. H. Holland : Mem. Geol. Surv. India, xxviii, Pt. 2,
1900, p. 134.
H. S. Washington: Am. Journ. Sci., xli, 1916, p. 323.
F. L. Stillwell : Aust. Ant. Exped. Set. Kef. A, iii i (i)
(Met. Rocks, Adelie Land), 1918, p. 193.
Charnockite Series, Holland, 1900. A series of rocks
resembling the pyroxene-granulites of Saxony,
ranging from charnockite through norite-like types
to pyroxenite and characterised throughout by the
presence of hypersthene.
Chassignite, Rose, 1863. -- An achondritic meteorite
essentially composed of olivine (enclosing chro-
mite) ; nickel-iron is absent, and the type thus
resembles the terrestrial dunite.
Chert. A more or less pure siliceous rock composed
in part of fibrous and radial chalcedony with or
without the remains of siliceous and other organ-
isms such as sponge spicules or radiolaria ; occur-
ring as independent formations and also as nodules
and irregular concretions in formations (generally
calcareous) other than the Chalk. The fracture is
THE NOMENCLATURE OF PETROLOGY 57
generally splintery rather than conchoidal. Cf.
W. Hill : Proc. Geol. Assoc., xxii, 1911, p. 61.
I E. F. Davis : Bull. Dept. Geol. Univ. Calijornia, xi, p.
Chiastolite-slate. A contact metamorphic rock, gener-
ally free from conspicuous cleavage or schistosity,
formed from carbonaceous shales, and containing
conspicuous crystals of chiastolite in a generally
Mem. Geol. Surv., 338 (Dartmoor), 1912, pp. 46 and 52.
A. Brammall : Geol. Mag., 1915, p. 224.
Chibinite, Ramsay, 1894. A coarse-grained variety
of eudialyte-syenite in which soda-amphiboles are
more abundant than soda-pyroxenes. It differs
from lujaurite in having a more granular texture,
and in containing rather less nepheline.
W. Ramsay : Fennia, xv, 2, p. 15.
China-clay. Although some ambiguity still exists as
to the exact use of the term china-clay, it is now
customary to regard it as a commercial term for
the clay obtained from China-clay Rock after wash-
ing. In Europe the term kaolin is sometimes used
for the clay both before and after washing. See
China-clay Rock. A term applied to thoroughly
kaolinised granite, essentially composed of quartz
and kaolin, and in Cornwall containing also gilber-
tite and white mica, and often tourmaline ; the
rock is soft and can easily be crumbled in the
J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and
China Stone), 1914, p. 12.
China-Stone. A term applied to any firm granitic rock
used in the manufacture of china, and usually,
but not necessarily, kaolinised ; the rock does not
crumble readily like china-clay rock ; Cornish
varieties contain white mica and fluorite.
J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and
China Stone), 1914, p. 135.
5 8 THE NOMENCLATURE OF PETROLOGY
Chladnite, Rose, 1863. A group name for achondritic
meteorites composed essentially of enstatite.
Brezina extended the term to include bronzite
stones of the diogenite group. To avoid confusion
Prior proposes the term Aubrite to replace Chlad-
nite as used by Rose and Tschermak.
Chlorite-SChist. -- A schist composed largely of
chlorite, the foliation being due to the parallel dis-
position of the flakes. Other minerals are gener-
ally present, such as quartz, epidote, magnetite
and garnet, the two latter being often in con-
spicuous idiomorphic crystals (porphyroblastic tex-
Chloritisation. -- The sum of the processes whereby
mafic minerals are altered to minerals of the
chlorite group, or whereby any minerals are re-
placed by chlorite.
G. H. Williams : U.S.G.S. Bull., 62, 1890.
ChlorQphyre, Dumont. -- A green variety of quartz-
diorite-porphyrite occurring at Lessines, Belgium.
Chondrite, Rose, 1864. A general term for meteoric
stones which contain chondrules (see below) em-
bedded in a finely crystalline matrix consisting
essentially of pyroxenes (mainly enstatite or
bronzite), olivine, and nickel-iron with accessory
troilite, chromite and oligoclase. Glass (? maske-
lynite) is sometimes present, and in the chondrules
may even become abundant. On the basis of the
ratio MgO/FeO in magnesium silicates and the
ratio Fe/Ni in nickel-iron, Prior has divided
chondrites into four groups containing respectively
the following percentages of nickel-iron : over 20 ;
between 20 and 10, between 10 and 6 and less
than 6. In these groups the proportion of nickel
steadily increases as the percentage of nickel-iron
decreases. See Table on p. 284.
G. T. Prior : Min. Mag., xviii, 1916, p. 26.
THE NOMENCLATURE OF PETROLOGY 59
Chondrules, Rose, 1864. Spheroidal aggregates,
often radiated in texture, varying in size from
microscopic dimensions to about that of a walnut,
which occur in many stony meteorites. The chief
minerals present are orthorhombic pyroxene and
olivine, with variable amounts of nickel-iron,
troilite, and oligoclase ; in some cases glass
(? maskelynite) of felspathic composition is an
Chonolith, Daly, 1905. A general term for injected
igneous intrusions, having shapes so irregular or
relations to the invaded formations so complex that
terms like dyke, laccolith, bysmalith, etc., are not
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 84.
Chrome-chert, Fermor, 1919. A variety of chert
which has replaced the silicate-minerals of a
chromite-peridotite, the more resistant chromite
grains remaining unaltered in the secondary
siliceous matrix. (Singhbhum, India.)
L. L. Fermor. : Proc. Asiatic Soc. Bengal, xv, 1919, p.
Ciminite, Washington, 1896. An olivine trachydoler-
ite containing phenocrysts of augite, olivine, and
orthoclase-mantled labradorite in a trachytic
groundmass. (Mt. Cimini, Italy.)
H. S. Washington : Journ. Geol., iv. 1896, p. 834.
Cipolino. A marble rich in silicate minerals, and
characterised more particularly by layers rich in
micaceous minerals. In France the term Cipolin is
used for crystalline limestones generally.
Clarain, Stopes, 1919. - - A term suggested for the
finely banded variety of " bright " coal. In
bituminous coals it occurs as bands of variable
thickness which have a smooth, shining surface
when broken at right angles to the bedding plane.
The type differs from vitrain in being minutely
banded and containing intercalations of fine
duratn. In thin section clarain appears translucent
60 THE NOMENCLATURE OF PETROLOGY
and shows a great variety of disintegrated plant
substances, bands of spores and other constituents,
the prevailing colours seen when the section is
sufficiently thin being tints of yellow to reddish-
Marie C. Stopes : Proc. Roy. Soc. B., xc, 1919, pp. 474-5.
Class, C.I.P.W., 1902. A division of igneous rocks
based on the relative proportions of the salic and
femic standard normative minerals as calculated
from chemical analyses. The descriptive terms
used, persalic, dosalic, salfemic, dofemtc, and per-
femic, correspond to the terms perfelsic, dofelsic,
mafelsic, domafic, and permafic, which are based
on the relative proportions of the felsic and mafic
minerals actually present. The division of
igneous rocks into classes is analogous to the less
rigid division into hololeucocratic, leucocratic,
mesocratic, melanocratic, and hclomelanocratic
FELSPARS F. C. Calkins : Journ. Geol., xxv, 1917, p. 157.
IGNEOUS INTRUSIONS R. A. Daly : Journ. Geol., xiii, 1905,
IGNEOUS ROCKS W. Cross : Q.J.G.S., Ixvi, 1910, p. 470.
A. Holmes: Geol. Mag., 1917, p. 115.
METAMORPHIC PROCESSES R. A. Daly: Bull. Geol. Soc. Ant.
xxviii, 1917. p. 375.
MINERALS W. H. Emmons : Econ. Geol., in, 1908, p. 611.
E. T. Wherry & S. T. Gordon : P*oc. A cad.
Nat. Sci., Philadelphia, 1915, p. 426.
ROCKS T. Crook : Min. Mag., xvii, 1914, p. 55.
VOLCANIC EXHALATIONS F. C. Lincoln : Econ. Geol., ii,
1907, p. 258.
For additional references see under individual subjects.
Clastic. A term applied to rocks composed of frag-
mental material derived from pre-existing rocks,
or from the dispersed consolidation products of
magmas (e.g., in explosion-tuffs and flow-
breccias). Cf. autoclastic, epiclastic, caiaclastic,
THE NOMENCLATURE OF PETROLOGY 61
Clay. - - An earthv deposit of extremely fine texture
which is usually plastic when wet, and becomes
hard and stone-like on being- heated to redness.
Chemically it is characterised by containing- hy-
drous silicates of alumina in considerable quantity,
with felspars and other silicates and quartz, and
variable amounts of carbonates and ferruginous
and organic matter. A proportion of the consti-
tuents is generally in the colloidal state, and then
acts as a lubricant to the grains and flakes of non-
E. R. Buckley : Wisconsin Geol. and Nat, Hist. Surv. Bull.,
vii, Pt. i, 1901.
H. Ries : Clays, Occurrence, Properties and Uses, 2nd Ed.,
New York, "1908.
J. W. Mellor : Trans. Ceramic Soc., viii, 1908.
H. E. Ashley: U.S.G.S., Bull. .388, 1909.
A. B. Searle : British Clays, Shales and Sands, London,
W. Salomon : Geol. Rund., vi, 1916, p. 398.
N. B. Davis : Trans. Amer. Inst. Min. Eng., li, 1916, p.
W. S. Boulton : Trans. Ceramic Soc., xvi, 1916-17, p. 237.
A. H. Cox : Geol. Mag., 1918, p. 56.
H. S. Washington : Journ. Am. Ceramic Soc., i, 1918, p.
Additional papers will be found in the Transactions of
the Ceramic Society.
Clay-ironstone. A term applied to sheet-like deposits
of concretionary masses of argillaceous siderite ;
associated with carbonaceous strata and particu-
larly with the Coal Measures.
Clay Rock. A term sometimes applied to indurated
Clay-slate. A variety of slate, the cleavage planes of
which are free from the lustre found in slates that
have attained a more crystalline condition, and
thus approach phyllite. The term also distin-
guishes argillaceous slates from those derived from
Claystone. An obsolete term for an altered felspathic
igneous rock, in which the whole rock or the
62 THE NOMENCLATURE OF PETROLOGY
groundmass has been reduced to a compact mass
of earthy or clayey alteration products.
Clay-with-FlintS, \Vhitaher, 1861. A deposit of
mixed chalk-flints and clay that lies directly on the
Chalk in many areas, and is often seen in pot-holes
or pipes. It is usually ascribed to the effect of
solution-weathering on chalk, but in many cases
there may be an additional admixture of Tertiary
materials. The clay is reddish or brown, very
tenacious, and often nearly black at the base of the
deposit, becoming- lighter and more sandy higher
up. Unfortunately the term has been loosely
applied to almost all the clay-flint drift deposits
that rest on the Chalk.
W. Whitaker : Mem. Geol. Surv. (Geology of London), Vol.
i, 1889, p. 281.
A. J. Jukes-Browne : Q.J.G.S., Ixii, 1906, p. 132.
R. L. Sherlock A. H. Noble : Q.J.G.S., Ixviii, 1912, p. 199.
G. Barrow : Prof. Geol. Assoc., xxx, 1919, p. 23.
Cleavage. (a) The property of minerals, due to their
atomic structure, whereby they can be readily
separated along planes parallel to certain possible
crystal faces, (b) The property of rocks such as
slates, which have been subjected to orogenic pres*
sure, whereby they can be split into thin sheets, the
plane of cleavage being at right angles or inclined
to the direction in which the pressure was applied,
according to the effects produced by shearing-
stress during the process.
A. Harker : Re-p. Brit. Assoc., 1885, p. 837.
G. F. Becker : Journ. Geol., vi, 1896, p. 429.
C. K. Leith : Structural Geology, 1914, p. 84.
Coagulation. A term applied to the process whereby
a homogeneous suspension of a colloidal substance
in a liquid settles down as a gelatinous mass ; i.e.,
the process whereby a sol passes into a gel. The
corresponding change in the case of a suspension
of minute granular material is termed floculation.
H. F. Ashley: U.S.G.S. Bull. 388, 1909, p. 15.'
THE NOMENCLATURE OF PETROLOGY 63
Coal. A general name applied to black carbonaceous
deposits, derived from accumulations of vegetable
debris which have been compacted by diagencsis
into firm brittle rocks exhibiting" a dull or shining
E. C. Jeffrey : Journ. Geol., xxiii, 1913, p. 218.
I). White & R. Thiessen : U.S.A. Bureau of Alines, Bull. 38,
A. Strahan & W. Pollard : Mem. Geol. Surv. (Coals, S.
W. Lomax : Trans. Inst. Min. Eng., liii, 1917, p. 137.
G. Hicklirig : Manchester Geol. and Min. Soc., 1918.
Marie C. Stopes & R. V. Wheeler : The Constitution of Coal,
Marie C. Stopes : Proc. Roy. Soc. B., xc, 1919, p. 472.
Coal-balls. -- Concretions of mineralised plant-debris
occurring in certain coal-seams.
Marie C. Stopes & D. M. S. Watson : Phil. Trans. Roy. Soc.
B., cc, 1908, p. 167.
Coefficient of Acidity, Vogt. The figure expressing
the following ratio, calculated from the molecular
proportions of the constituents of a rock or slag
Number of atoms of oxygen in SiO z .
Number of atoms of oxygen in the basic oxides.
Cognate Inclusions, Harker, 1900. A term applied
to xenocrysts or xenoliths occurring in an igneous
rock to which they are genetically related ; = en-
claves homceogenes autoliths.
A. Harker : Journ. Geol., viii, 1900, p. 389.
Cokeite, Lacroix, 1910. Natural coke formed by the
action of magmas on coal, or by natural combus-
tion of coal in mines.
A. Lacroix : Min. de la France, iv, 1910, p. 648.
Collobrierite, Lacroix, 1917. -- A metamorphic rock
composed of grunerite, fayalite, garnet, and mag-
netite. (Collobrieii, France.)
A. Lacroix : Bull. Soc. franf. Min., xl, 1917, p. 62.
Colloids. Microheterogeneous substances composed
of two phases, one of which is dispersed through
the other; e.g., a jelly in which one phase forms a
THE NOMENCLATURE OF PETROLOGY
continuous cellular framework, while the other, a
liquid, occupies the pores.
Dispersed systems may be molecular, colloidal,
or coarse ; colloidal systems are denned as those in
which the diameters of the dispersed particles lie
between i/x/z and ioo/z/j, (i.e., 1/1,000,000 mm. and
i/ 10,000 mm.), and they are distinguished from
molecular solutions by not dialysing, and from
coarse dispersions by the fact that their individual
particles cannot be distinguished microscopically.
Liquid colloids are known as sols, and their coagu-
lation products as gels. Coagulation is the result
of a decrease in the degree of dispersion ; peptisa-
tion that of an increase in the degree of dispersion.
The following table gives examples of different
types of dispersed systems :
s = solid "\ ,. j (S = solid.
s + S
s + L
s + G
1 + S
1 + L
Water of crystal-
g + s
g + L
g + G
H. E. Ashley : U.S.G.S. Bull. 388, 1909.
A. F. Rogers : Journ. Geol., xxv, 1917, p. 515.
W. Ostwald (trans, by M. H. Fischer) : Theoretical and
Applied Colloid Chemistry, 1917.
E. Hatschek : Introduction to the Physics and Chemistry of
THE NOMENCLATURE OF PETROLOGY 65
Colour Ratio, Shand, 1915. The ratio of felsic (light)
to mafic (dark and heavy) minerals in an igneous
rock, which thus accurately expresses the leuco,
meso-, or melano-cratic character of the rock.
S. J. Shand : Journ. GeoL, xxiv, 1916, p. 403.
Columnar Structure. A structure found in lava flows,
sills, and dykes, and most characteristically deve-
loped in basaltic rocks, due to the regular develop-
ment of prismatic joints that break up the rock
into parallel columns, the sides of which average
six in number. Analogous prismatic structures
sometimes occur in rocks other than igneous.
T. G. Bonney : Q.J.G.S., xxxii, 1876, p. 140.
E. M. Kindle : GeoL Surv. Canada, Mus. Bull. 2, 1914,
R. B. Sosman : Journ. GeoL, xxiv, 1916, p. 215.
C. Dauzere : C.R. clxix, 1919, p. 76.
Comagmatic, Washington, 1906. A term applied to
igneous rocks (or to the district in which they
occur) characterised by chemical and mineral pecu-
liarities which point to consanguinity or com-
munity of origin. The term Comagmatic Region
according to Washington is wider than Petrogra-
phical Province (Judd), since " province " implies
that the area is part of a larger one, and " petro-
graphical " does not include petrological charac-
ters and relations.
H. S. Washington : Carnegie Inst. Wash., Pub. 57, 1906,
Comendite, Bertolio, 1895. An alkaii-rhyolite con-
taining soda-pyroxenes and/or soda-amphiboles.
G. T. Prior : Min. Mag. y xiii, 1902, -p. 242.
Complementary Dykes, Brdgger, 1894. Associated
dykes (or other minor intrusions) composed of
different but related rocks regarded respectively as
hucocratic and melanocratic differentiation pro-
ducts from a common magma (e.g. , aplites and
lamprophyres ; bostonite and camptonite).
VV. C. Brogger : Q.J.G.S., 1, 1894, p. 31.
66 THE NOMENCLATURE OF PETROLOGY
Component. In the phase rule this term denotes each
of the integral parts (independent molecular species
not connected by a chemical equation), of which a
system is composed, and in terms of which the
system may be described (e.g., the system CaO,
A1 2 3 , Si0 2 ).
Composite DykCJS, Judd, 1893. Dykes consisting of
two or more injections of magmas having different
compositions. The term composite is similarly
applied to sills, laccoliths and other intrusions.
Mem. Geol. Surv. Scot., 53 (Ben Nevis and Glen Coe), 1916,
A. Harker : Mem. Geol. Surv. Scot. (Tert. Ig. Rocks Skye),
1904, p. 197.
W. R. Smellie : Trans. Geol. Soc. Glasgow, 1913, p. i.
Composite Gneiss. Gneisses produced by the inti-
mate association, with or without molecular inter-
mixture, of two different materials, the one (gene-
rally a granitic magma) having been injected into
the other (e.g., along the parting planes of a
G. A. J. Cole : Proc. Roy. Irish Acad., xxiv, 1902, p. 203.
Concretions. Nodular or irregular concentrations of
certain authigenic constituents of sedimentary
rocks and tuffs ; developed by the localised deposi-
tion of material from solution, generally about a
central nucleus; e.g., septaria, flint, nodules of
marcasite or iron-pyrites,- loss puppchen, kankar,
G. F. Becker : U.S.G.S., Mon., xiii, 1888, p. 64.
R. Delkeschamp : Zeit. f. Prakt. Geol., xii, 1904, p. 289."
W. A. Richardson: Min. Mag., xviii, 1919, p. 327.
Cone-in r COne Structure. A concretionary structure
occurring in marls, ironstones, coals, etc., char-
acterised by the development of a succession of
cones one within another, due to radial crystallisa-
tion about a common axis.
G. A. J. Cole : Min. Mag., x, 1892, p. 136.
Conglomerate. A cemented clastic rock containing
rounded fragments corresponding in their grade
THE NOMENCLATURE OF PETROLOGY 67
sizes to gravel or pebbles. Monogenetic and poly-
genetic types are recognised, according to the uni-
formity or variability of the composition and
source of the pebbles.
G. R. Mansfield : Bull. Museum CQin-p. Zoology Harvard,
xlix, Geol. Ser., viii, No. 4.
J. W. Gregory : Geol. Mag., 1915, p. 447.
W. Deeke : Ber. Naturjor. Gesell., xxii, (i), 1919.'
Congressite, Adams & Barlow, 1913. A hololeuco-
cratic coarsely granular igneous rock composed
mainly of nepheline, with small amounts of soda-
lite, plagioclase, micas, calcite, and titanoferrite.
(Congress Bluff, Craigmont Hill, Ontario.)
F. D. Adams & A. E. Barlow : Cong. GeoL Inter., xii,
Guide 2, 1913, p. 96.
Connate, Lane, 1908. A term applied to waters (and
extended to include CO 2 in limestones, and other
volatile materials) buried with exogenetic forma-
tions and volcanic rocks, and remaining stagnant
except as they are liberated by diagenesis or meta-
A. C. Lane : Bull. Geol. Soc. Am., xix, 1908, p. 502.
Consanguinity, Iddings, 1892. A term implying
" blood relationship," or community of origin, in
the rocks of a single volcanic or petrological dis-
trict or province, and revealed by common pecu-
liarities of mineral and chemical composition, and
often also of texture. Cf. Petro graphical Province.
J. P. Iddings : Bull. Phil. Soc. Wash., xii, 1892, p. 89.
Consertal, C.I.P.W., 1906. A term applied to equi-
granular texture, when irregularly-shaped crystals
closely interlock without interstitial spaces.
C.l.l'.W. : Jouru. Geol., xiv, 1906, p. 703.
Contact (or Local) Metamorphism. Metamorphism
genetically connected with the intrusion (or extru-
sion) of magmas, i.e., the alteration of rocks re-
ferred to their contact with or proximity to, a body
of igneous rock. It is probable that in most cases
of contact metamorphism the depth at which
alteration took place was moderate, whereas in
68 THE NOMENCLATURE OF PETROLOGY
regional metamorphism (also in part due to mag-
matic transfer of heat) the depth was greater. Cf.
exomorphic and endomorpliic metamorphism.
Mems. Geol. Surv. (Silurian Rocks, Britain), I, 1899, p. 634;
(Ben Nevis and Glen Coe), 1916, p. 187 ; (North-West High-
lands), 1907, p. 453.
[. M. Clements : Am. Journ, Sci., vii, 1899, p. 81.
r . M. <Goldschmidt : Die Kontakt Met am or -phase itn Kris-
Contemporaneous. A term applied to interbedded
volcanic rocks (contrasting them with sills of later
date than the enclosing rocks) ; to segregation
veins and patches (cf. schlieren) in bodies of ig-
neous rocks ; to dolomites produced from lime-
stones soon after the deposition of the latter ; and
generally, to all rocks and facies developed while
the processes of formation of the enclosing rocks
were still in operation.
Convection. - - The internal circulation within a fluid
mass set up by differences of density in different
parts of the mass owing to changes in temperature
or phase. For the application to magmas, see
F. F. Grout : Journ. Geol., xxvi, 1918, p. 481.
C. H. Desch : Journ. Inst. Metals, xi, 1914, p. 77.
Coppaelite, Sabatini, 1903. -- A porphyritic volcanic
rock composed of phenocrysts of augite in a holo-
crystalline groundmass of pyroxene, melilite,
phlogopite and small amounts of perovskite and
apatite. (Coppaeli di Sotto, Umbria.)
Coprolite. The fossilised excrement of fishes, reptiles
and mammals. As these remains are largely com-
posed of calcium phosphate, the term applied to
them has been commercially extended to include
Coquina. A loosely cemented fragmental shelly lime-
stone occurring in Florida.
Coral Mud and Sand. Deposits formed around coral-
islands and coasts bordered by coral-reefs, contain-
ing abundant fragments of corals. Near the reefs
the grade sizes are relatively coarse, and the
THE NOMENCLATURE OF PETROLOGY 69
deposit is described as coral-sand, whereas further
out, the grades become gradually finer until the
material is a coral-mud.
J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea
Deposits), 1891, p. 244.
Cordierite-anthophyllite Rock, Eskola, 1914. A
pneumatolytic-metamorphic rock consisting essen-
tially of anthophyllite (as radiating bunches or irre-
gularly distributed prisms) and cordierite. Other
minerals, such as biotite, garnet, quartz, plagio-
clase and magnetite, may be present in varying
amounts, and by increase in plagioclase the type
passes into plagioclase-gneiss.
P. Eskola : Bull. Comm. Geol. Finlande, 40, 1914, pp. 169,
Cordierite-norite, Lacroix, 1898. A term applied to
endomorphic varieties of norite containing cor-
dierite. Cf. Mtiscovadite.
A. Lacroix : Butt. Serv. Carte Geol. France, No. 67, x, 1898-
W. R. Watt : Q.J.G.S., Ixx, 1914, p. 285.
For Cordierite in general, see
J. J. H. Teall : Proc. Geol. Assoc., xvi, 1899, p. 62.
Cornstone. A term applied to the concretionary and
other limestone masses associated with the Old
. Red and the New Red Sandstone formations.
Their presence increases the fertility of the soil
derived from the formations in which they occur,
and hence the name.
Cornttbianite, Boase, 1832. -- A term applied to
finely granulose rocks of horny aspect (hornfels),
formed by contact metamorphism, and consisting
of micas, quartz, and felspar. Cf. Leptynolite.
( Cornubia = Cornwall. )
T. G. Bonney : Q.J.G.S., xlii, 1886, p. 104.
W. Salomon : Cong. Geol. Inter. C.R., viii (Paris, 1900).
1901, p^. 343.
Corona (Coronite, Brdgger). A term applied to zones
of radially-arranged minerals (e.g., of pyroxene
amphibole, garnet, etc.) that occur around olivine
or hypersthene in certain gabbros, norites- and re-
70 THE NOMENCLATURE OF PETROLOGY
lated rocks. They may be metamorphic reaction
rims, or due directly to the order of crystallisation,
and thus of igneous origin. It has been suggested
by Bonney that the term Kelyphitic rim be
restricted to occurrences of secondary origin, leav-
ing Corona for those that are primary.
Corrosion. The modification of phenocrysts or
xenoliths, etc., by the solvent action* upon them of
the residual magma in which they are contained.
The same term (corrasicn of some American
authors) connotes the vertical excavation of the
land by rivers and glaciers.
P. Eskola : Bull. Comm. Geol. Finlande, 40, 1914, p. 22.
Corsite, Collomb, 1853. - - A well-known variety of
orbicular diorite or hornblende-gabbro occurring in
Cortlandtite, Williams, 1886. Hornblende-peridotite
= Hudsonite. The type variety contains horn-
blende in large crystals, with poikilitically-in-
cluded crystals of olivine.
(Cortlandt, New York.)
G. S. Rogers : Ann. N. York Acad. Set., xxi, 1911, p. n.
Corundolite, Wadsworth, 1891. A systematic term
proposed for emery-rock.
Country Rock. -- A general term for the rock sur-
rounding and penetrated by mineral veins ; some-
times used in a wider sense for the rocks invaded
by igneous intrusions.
Covite, Washington, 1900. A somewhat melanocratic
variety of nepheline-syenite, in composition falling
between the latter and shonkinite.
(Magnet Cove, Arkansas.)
H. S. Washington : Journ. Geol., ix, 1901, p. 612.
Craiglockhart Basalt, Hatch, 1892. -- A type of the
Scottish Carboniferous basalts ; characterised by
the presence of conspicuous phenocrysts of olivine
and augite in a fine-grained basaltic groundmass.
E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), 1910,
THE NOMENCLATURE OF PETROLOGY 71
Craigmontite, Adams & Barloiv. -- A leucocratic
facies of nepheline-syenite, containing in order of
abundance, nepheline, oligoclase, and muscovite,
with small amounts of calcite, corundum, biotite
and magnetite. (Craigmont Hill, Ontario.)
F. D. Adams & A. E. Barlow : Geol. Surv. Canada Mem.,
6 (Pub. No. 1,082), 1910, p. 313.
Crinanite, Flett, 1911. A variety of olivine-analcite-
dolerite, containing purple augite, and char-
acterised by well-developed ophitic texture.
(Loch Crinan, Argyll.)
Mem. Geol. Surv. Scot. (Colonsay), 1911, p. 35.
Cromaltite, Shand, 1906. An alkali pyroxenite, con-
taining aegirine-augite, melanite and biotite.
(Cromalt Hills, Assynt.)
, S. J. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 394.
Crush-breccia, Bonney. A cataclastic breccia formed
in or nearly in situ by mechanical fragmentation.
Crush-conglomerate, Lamplugh, 1895. A cataclastic
conglomerate formed by mechanical fragmentation
and friction, due to earth-stresses.
G. W. Lamplugh: Q.J.G.S., li, 1895, p. 563.
Cryptocrystalline (Microcryptocrystalline of some
American authors). A term implying that a rock
or groundmass is composed of a crystalline aggre-
gate that can only be recognised as such by its
appearance in thin section between crossed nicols ;
individual minerals not being directly determinable.
Cryptographic, Harker, 1895. A texture, often
radial, due to the intergrowth of quartz and felspar
on so fine a scale that the individual component
minerals cannot be clearly resolved under the
microscope ; a cryptocrystalline granophyric
Crystal. A body, generally solid, but not necessarily
so, whose, component atoms are arranged in
definite space lattices, crystal faces being a com-
72 THE NOMENCLATURE OF PETROLOGY
monly developed outward expression of the
periodic arrangement of atoms.
W. H. and W. L. Bragg : X-Rays and Crystal Structure,
I 9 I 5-
F. E. Wright : Journ. Wash. Acad. Sci., vi, 1916, p. 326.
Crystalline Limestone. -- A general term for meta-
morphosed limestones, the mineral composition
depending on the character of the original lime-
stone, the thermo-dynamic conditions under which
the metamorphism was effected, and the amount
and composition of material (if any) introduced
from external sources. See calciphyre, cipolino,
marble, ophicalcite, predazzite, etc. A limestone
recrystallised by diagenesis is described as recrys-
A. K. Coomaraswamy : Q.J.G.S., li, 1902, p. 399; lix, 1903,
J. J. H. Teall: Mem. GeoL Stirv. (N.W. Highlands), 1907,
A. S. Eakle : Butt. De-pt. Geol. Univ. California, x, 1917,
Crystalline Schist. See Schist.
For References see under Metamorphism.
Crystal linity. A term applied to the degree of
crystallisation exhibited by an igneous rock ; ex-
pressed by terms such as holo crystalline, hypo-
crystalline, holohy aline, etc.
Crystallisation. - The process whereby crystalline
phases separate from a fluid, viscous, or dispersed
state (gas, liquid solution, or rigid solution).
G. F. Becker & A. L. Day : Journ. GeoL, xxiv, 1916, p. 313.
F. E. Wright : Journ. Wash. Acad. Sci., vi, 1916, p. 326.
Crystallite, Vogelsang, 1870. - - A general term for
minute bodies without reaction on polarised light,
occurring in glassy igneous rocks : e.g., globulite,
longulite, margarile, trichite, and other forms of
incipient crystallisation that cannot be referred to
definite mineral species.
F. Rutley : Min. Mag., ix, 1891, p. 261.
C, H. Desch : Journ. Inst. Metals, xi, 1914, p. 65.
THE NOMENCLATURE OF PETROLOGY 73
Crystalloblastic, Becke, 1903. A term applied to the
textures of metamorphic rocks due to recrystallisa-
tion under conditions of high viscosity and
directed pressure, in order to distinguish them
from the textures of igneous rocks, which are due
to the successive crystallisation of- minerals under
conditions of relatively low viscosity and nearly
F. Becke : Cong. Geol. Inter. C.R., ix, 1903, p. 553.
U. Grubenmann : Die Kristallinen Schiefer, I, 1904.
F. L. Stillwell : Aust. Ant. Ex-ped. Sci. Reft. A, iii, T (i)
(Met. Rocks, Adelie Land), 1918, p. 40.
Crystal Tuffs, Cohen, 1871. - - Volcanic tuffs, which
are largely composed of crystal fragments. Cf.
vitric and lithic tuffs.
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191.
Cltcalite, Rolle, 1879. - - A variety of diabase char-
acterised by abundant chlorite and passing locally
into chlorite-schist. (Rhsetic Alps.)
Culm. A vernacular term variously applied according
to the locality, to carbonaceous shale, or to fissile
varieties of anthracitic coal. The term has also a
definite stratigraphical meaning for beds of
Pendleside and Westphalian age.
Cumber landite, Wadsworth, 1884. A phanerocrys-
talline rock composed of ferriferous olivine,
ilmenite and magnetite, with small amounts of
labradorite and spinel.
(Iron Mine Hill, Cumberland, Rhode I.)
Cumbraite, Tyrrell, 1917. A porphyritic rock, con-
taining phenocrysts of bytownite-anorthite in a
groundmass of labradorite,, enstatite-augite and
abundant glass ; and in chemical composition cor-
responding to andesite rather than to basalt.
(Great Cumbrae, Firth of Clyde.)
G. W. Tyrrell : Geol. Mag., 1917, p. 306.
Cumulite, Vogelsang, 1872. A term applied to cloudy
aggregates of globulites occurring in vitreous
F. Rntley : Min. Mag., ix, 1891, p. 261.
74 THE NOMENCLATURE OF PETROLOGY
Cumulophyric, C.I.P.W., 1906. A term applied to
glomeroporphyritic texture in the widest sense,
i.e., when the clusters of crystals forming com-
posite phenocrysts are not necessarily aggregates
of the same mineral.
C.T.P.W. : Joitrn. Geol., xiv, 1906, p. 703.
Cumulose Deposits, Merrill, 1897. - - Sedentary
accumulations of carbonaceous matter, with very
little detrital sediment, e.g. , peat, swamp-soil.
Cup-and-ball Structure, A cross jointing of columnar
igneous rocks, in which one face of the joint is
concave and the other convex ; as in the columns
of the Giant's Causeway.
Cupola, Daly, 1911. A dome- or boss-like protrusion
from the body of a batholith, forming a con-
spicuous irregularity in its roof.
Current- or Cross-bedding. A structure of sedi-
mentary rocks, generally arenaceous, in which the
planes of deposition, as shown by the arrangement
of the grains in successive layers, lie obliquely to
the planes separating the larger units of stratifica-
tion. The structure is commonly developed in
aeolian, deltaic and torrential deposits, each of
which has its own distinctive characters.
Cuselite, Rosenbvsch t 1887. A term applied to leuco-
cratic varieties of biotite-augite-porphyrite con-
taining abundant phenocrysts of andesine and few
of the mafic minerals, in a felspathic groundmass.
(Cusel, Saar Basin.)
Dacite. Quartz-andesite. According to the composi-
tion of the plagioclas-e, three different types of
dacite are distinguished by Iddings : Ungaite
(oligoclase), Shastaite (andesine), and Bandaite
(labradorite). The last of these would generally
be regarded as a variety of quartz-basalt.
H. H. Robinson: U.S.G.S., Prof. Pa$., 76, 1913, p. 114.
THE NOMENCLATURE OF PETROLOGY 75
Dacitoid, Lacroix, 1919. A volcanic rock having the
chemical composition of dacite but free from
A. Lacroix : C.R., xlxviii, 1919, p. 297.
Dactylitic, Sedefholm, 1916. A textural term applied
to finger-like projections from a continuous crystal,
the fingers (e.g., of biotite) and the intercalated
mineral between them (e.g. , of quartz) together
forming a symplektite, q.v.
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48,
1916, Figs. 32-4, PI. vi.
Dactylotype, Shand, 1906. A textural term applied
to the intergrowth of sodalite with orthoclase in
borolanite and its associates ; the sodalite has been
altered to pinitic mica and appears in thread-like or
vermicular aggregates closely packed in a matrix
S. J. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 387, PI. 39.
Dahamite, Pelikan, 1902. A variety of paisanite
characterised by the presence of abundant albite.
Dalmeny Basalt, Hatch, 1892. A type of the Scottish
Carboniferous basalts ; characterised by the abund-
ance of microphenocrysts of olivine, augite and
plagioclase being restricted almost always to the
J. D. Falconer : Irans. Roy. Soc. Edin., xlv, 1906, p. 133.
Damouritisation, Lacroix, 1896. The process where-
by the aluminous silicates (felspars, etc.), of a rock
are transformed into damourite (a variety of mus-
A. Lacroix : Min. de la France, n, 1896, p. 41.
Davainite, Wyllie & Scott, 1913. A rock consisting
essentially of brown hornblende which is para-
morphic after pyroxene, the amount of other
minerals, such as felspar, being small.
B. K. N. Wyllie & A. Scott : Geol. Mag., 1913, p. 499.
7 6 THE NOMENCLATURE OF PETROLOGY
Dedolomitisation, Teall. -- A process whereby a
dolomite, during metamorphism, loses its content
of magnesium carbonate, the magnesium remain-
ing as oxide or hydroxide (e.g., in pencatite) Qt
as a silicate (e.g., in forsierite marble, ophicalcite,
etc.). It is not desirable to extend the term, as
has recently been suggested, to include the re-
moval of dolomite mechanically.
J. J. H. Teall : Geol. Mag., 1903, p. '513.
A. Harker : Mem. Geol. Si:rv. (Tert. Ig. Rocks Skye), 1904,
J. J. H. Teall: Mem. Geol. Siirv. Scot. (X.\V. Highlands),
1907, p. 453.
F. H. Hatch & R. H. Rastall : Q.J.G.S., Ixvi, 1910, p. 507.
T. Crook : Geol. Mag., 1914, p. 339.
of Freedom. The number of physical condi-
tions, including temperature, pressure, and con-
centration, that can be varied independently in a
system without destroying a phase.
Dellenite, Brogger, 1896. - - A volcanic rock inter-
mediate between rhyolite and dacite, i.e., contain-
ing both orthoclase and oligoclase-andesine ; =
quartz-latitc = quartz-trachyaiidesite.
(Lake Dellen, Sweden.)
Density. The density of a substance is the weight (ex-
pressed in grams) of unit volume (one cubic centi-
metre) of the substance at 4 C. Cf. Specific
A. L. Day et aliter : Am. /. Sci., xxxvii, 1914, p. i.
A. Holmes : PetrograpJric Methods and Calculations, 1920.
Denudation, Poullet-Scrope, 1825. - - The sum of the
processes that result in the wearing down of the
surface of the earth. The term is wider in its
scope than erosion, the restriction proposed by
Lyell (limiting it to the action of running water)
not having been generally adopted.
J. W. Gregory : Geog. Journ., xxxvii, 1911, p. 189.
J. W. Evans : Proc. Geol. Assoc., xxiv, 1913. p. 241 ; xxv,
1914, p. 229.
THE NOMENCLATURE OF PETROLOGY 77
Derivate, Forbes, 1867. A general term for "sedi-
mentary " rocks derived from the products of
destruction of primary rocks. Cf. Ingenite.
Dermolith, Jag gar, 1917. A term, meaning " skin-
stone," applied to ropy-lava or pahoehoe-lava.
T. A. Jaggar : Jour. Wash. Acad. Sci., vii, 1917.
Desmosite, Zincken, 1841. A contact metamorphosed
shale or slate differing from spilosite by having a
Detritus. -- Fragmented (epiclastic) material, such as
sand and mud, derived from older rocks by dis-
integration. The deposits produced by the
accumulation of detritus constitute the detrital
Deuteric, Sederholm f 1916. A term applied to altera-
tions in an igneous rock produced during the later
stages, and as a direct consequence, of the con-
solidation of the magma of the rock. (Cf. Paulo-
post.) The term discriminates such alterations
from the more strictly secondary changes due to a
later period of alteration.
j. J. Sederholm : Bull. Couim. Geol. Finlande, No. 48, 1916,
DeuterogeriOUS, Naumann, 1858. A group name for
"derived" rocks; used more definitely by Rene-
vier, 1880, for sedimentary rocks of mechanical
Deuteromorphic, Loewin3Qn-Lessing J 1897. A general
term applied to crystals to indicate that their
shapes have been acquired or modified by the action
of mechanical or chemical processes on the forms
which they originally possessed. Deuteromorphic
forms are described as tectomorphic when the
modifications are due to magmatic corrosion ; as
lytomorphic, when due to aqueous solutions ; as
schizomorphic, when due to cataclastic processes ;
as clastomorphic, when due to denudation as in the
rounded or angular grains of a detrital sediment ;
and as neonwrphic when any one of the preceding
78 THE NOMENCLATURE OF PETROLOGY
types has been regenerated by zones of secondary
growth in crystalline continuity.
Devitrification. The process by which glass (natural
or artificial) develops a minutely crystalline or
lithoidal texture, and becomes microfelsitic or
microspherulitic. Devitrification is an expression
of solid diffusion, promoted by crystal forces so
long as the latter are not inhibited by internal
T. G. Bonney & J. Parkinson : Q.J.G.S., ix, 1903, p. 429.
N. L. Bowen : Journ. Am. Ceramic Soc., ii, 1919, p. 261.
DeVOnite, Johannsen, 1910. A variety of porphyritic
dolerite characterised by phenocrysts of plagio-
clase rich in potassium. (Mt. Devon, Mass.)
Diabase, Brongniart, 1807. This term originally de-
noted rocks that were later recognised by Haiiy
as diorites. (Conversely, in many of the older
geological maps of Ireland, rocks are named
diorite that would now be called diabase.) For a
time the term diabase was applied to pre-Tertiary
dolerites, and since, especially in Britain, such
rocks are frequently altered, the term has come to
mean an altered dolerite in which the felspars are
saussuritised or albitised, or the pyroxenes more
or less replaced by hornblende or chlorite. Ger-
man and most American authors, however (follow-
ing Rosenbusch), use diabase in a sense synony-
mous with the British usage of dolerite.
Diablastic, Becke, 1903. See Sieve Texture.
Diagenesis, Gumbel, 1888. A term denoting the sum
of the successive changes which take place in
exogenetic rocks as a result of continued sedi-
mentation above them, or of the percolation of
ground-waters through them; e.g., consolidation,
development of lamination by increase of vertical
pressure due to the superincumbent load, and
cementation and recrystallisation due to seasonal
THE NOMENCLATURE OF PETROLOGY 79
and other regular changes in water content and
temperature of a normal exogenetic character.
E. Andree : Geol. Rund., iii, 1912, p. 324.
W. Deeke : Ber. Naturfor. GeselL, xxii, (i), 1919.
Diallagite, Des Cloizeaux, 1863. -- A rock composed
almost wholly of diallage. Small amounts of
other pyroxenes, hornblende, pleonaste, or garnet
may be present.
Diamagnetism, Faraday, 1845. A property of certain
substances -- essentially different from ferro-
magnetism and paramagnetism in virtue of
which, when placed in a non-uniform magnetic
field, they tend to move towards the weakest part.
Unlike ordinary magnetic bodies the molecule has
either no inherent polarity or has a balanced
polarity. In a magnetic field the induced polarity
leads to repulsion, arid diamagnetic susceptibility
is therefore negative. Cf. Paramagnetism.
T. Crook : Science Progress, No. 5, 1907, p. 30.
DiaschistlC, Brogger, 1896. A term applied to those
rocks of minor intrusions which appear to be
respectively melanocratic or leucocratic dif-
ferentiates from a common magmatic source.
Diatomite, Diatomaceous Earth. A pulverulent
siliceous deposit formed by the accumulation of the
frustules of diatoms in lakes or swamps ; = Tripoli
Diatom Ooze, Murray, 1873. A deep-sea deposit, re-
sembling flour when dry, largely composed of the
frustules of diatoms, and containing a small but
variable proportion of calcareous organisms and
J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea
Deposits), 1891, p. 208.
Diatreme. - - A general term for volcanic pipes and
vents drilled through the enclosing rocks by the ex-
plosive energy of gas-charged magmas.
W. Branca : Schwaben 125 Vulcanembryonen , Stuttgart,
So THE NOMENCLATURE OF PETROLOGY
Differential Pressure. See Directed Pressure.
J. Johnston & P. Niggli : Journ. GeoL, xxi, 1913, p. 614.
Differentiated (S/77, Dyke, TMccoHth, Batholith, etc.}.
A term applied to major and minor intrusions
that are built up of two or more rock-types that
have developed in situ by differentiation from a
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 229,
and Table xiv, p. 230.
Differentiation. - - A general term for the processes
whereby different types of igneous rocks, which
may or may not form parts of the same mass, are
produced from .a common magmatic source ; the
processes involved may be molecular, or the
separation of immiscible liquids, or the separation
of residual liquids from crystals already formed ;
and the interactions between units of differentia-
tion formed at one time or place with those formed
at other times or places must also be considered,
and especially in relation to thermo-dynamic con-
ditions and the presence of volatile fluxes.
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 334.
See also S. J. Shand : An Introduction to Petrology, etc.
(Royal Scottish Museum, Edinburgh), 1909, p. 43, for
a summary account of Brogger's work and its results.
H. S. Washington : Journ. GeoL, ix, 1901, p. 645.
A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 309.
Cong. GeoL Inter. C.R.. xii (1912), 1913, p. 189.
H. S. Jevons : Journ. Roy. Soc. N.S.W., xlvi, 1913, p. 112.
N. L. Bowen : Am. Journ. Sci., xxxix, 1915, p. 175 ; xl,
1915, p. 161.
- Joi4rn. GeoL, Supplement to xxiii, 1915, p. 3.
A. Holmes : Q.J.G.S., Ixxii, 1917, p. 271.
R. A. Daly: Journ. GeoL, xxvi, 1918, p. 115.
F. F. Grout : Journ. GeoL, xxvi, iqrS, p. 626.
H. H. Read : GeoL Mag.. 1919, p. 368; 1920, p. 86.
N. L. Bowen : Journ. GeoL, xxvii, 1919, p. 393.
Diffusion. The permeation of one substance through
another ; such as gas through gas, liquid or solid ;
solute through solvent, liquid through liquid or
solid, and finally solid through solid. The pres-
THE NOMENCLATURE OF PETROLOGY 81
sure corresponding to that exerted by dissolved
material in its diffusion from a more concentrated
to a less concentrated part of a solution is called
R. F,. Liesegang : GeologiscJie Diffttsionen, 1913.
C. H. Desch : Re-p. Brit. Assoc. (Dundee, 1912), 1913, p. 348.
C. E. Van Orstand & F. P. Dewey : U.S.G.S., Prof. Pa-p.,
95, iQ^. P- 8 3-
Diluvium. An old term by which the older Quarter-
nary or Pleistocene deposits were described in con-
tradistinction to the young-er Quarternary or
Recent deposits laid down by rivers (alluvium).
The term diluvium refers to the Deluge of Noah to
the action of which the deposits were originally
supposed to be due.
Diogenite, Tschermak, 1883. - - An achondritic
meteorite composed essentially of bronzite with
small amounts of oligoclase ; = oHgoclase chlad-
Diorite. D'Aubuisson, 1819. - A phanerocrystalline
igneous rock composed of plagioclase (averaging
andesine, or occasionally oligoclase) and mafic
minerals such as hornblende, biotite, and augite,
hornblende being especially characteristic. If
quartz be present the term qitartz-dioritc is used.
The term diorite means " a clear distinction " as
opposed to dolerite, which means " deceptive."
In Ireland many altered rocks, such as diabase
and epidiorite, have been described as diorite on
the older maps. Cf. Laugenite.
Dipyrisation, Lacroix, 1896, = Scapolitisation. The
process, sometimes involving pneumatolytic or
allied agencies, whereby the felspathic constituents
of a rock are replaced by dipyre or scapolite.
N. Sundius : Geologie des Kirunagebietes, Upsala, 1915, P-
A. Lacroix : Bull. Soc. fran$. Min., 1916, p. 74.
Directed Pressure, Evans, 1919. A term suggested
in place of the terms " unequal," " non-uniform "
82 THE NOMENCLATURE OF PETROLOGY
or " differential " pressure to denote the maximum
stress-difference acting- on any system, and which,
unlike hydrostatic or " uniform " pressure
operates in a definite direction. Thus a compres-
sion, and in general any natural pressure is resol-
vable into hydrostatic pressure, and directed
pressure. The latter can have little effect on the
properties of liquids beyond causing- them to flow ;
but acting on solids, it modifies old structures and
tends to the production of new ones, ranging in
the case of rocks from mountain building" to
microscopic granulation., and leading finally to re-
crystallisation. During- dynamic metamorphism
the behaviour of crystalline bodies is controlled by
both the hydrostatic and directed components of
pressure whereas fluid phases are subject to
the action of the former component only. Under
these conditions the melting or volatilisation points
of solids are lowered, locally and momentarily, and
thus recrystallisation and diffusion are promoted.
The study of dynamic metamorphism is essentially
the study of the modifications effected in rocks by
J. Johnston & P. Niggli : Journ. Geol., xxi, 1913, p. 599.
J. Johnston : Journ. Geol., xxiii, 1915, p. 732.
A. Harker : Q.J.G.S., Ixxiv, 1918. p. Ixxvii.
J. W. Evans : Nature, civ, Oct. and, 1919, p. 106.
Ditroite, Zirkel, 1866. A variety of nepheline-syenite
containing sodalite among the felsic constituents,
and biotite and aegirine-augite among the mafic
minerals, with zircon and perovskite as note-
worthy accessories. By Brogger, the term has
been adopted to include all nepheline-syenites of
granular texture, as opposed to those of trachytoid
texture (foyaite). (Ditro, Transylvania.)
Do-, C.I.P.W., 1902. -- A prefix indicating that one
factor dominates over another within the ratios 7/1
an d 5/3 (7 and 1.67); e.g., docalcic, dofemic,
THE NOMENCLATURE OF PETROLOGY 83
Dolerine, Jurine. A variety of talc-schist containing
felspar and chlorite as the chief varietal minerals.
Dolerite, Hauy. An igneous rock occurring as minor
intrusions, consisting essentially of plagioclase
(not less calcic than labradorite), and pyroxene.
Olivine-bearing types are distinguished as olivine-
dolerite. In a general way dolerite is distinguished
from basalt by its coarser grain and the absence
of glassy specifically, according to the defini-
tion of the Comit^ francaise de Petro graphic, 1900,
by its holocrystalline character and the develop-
ment of ophitic texture. In practice, however,
there are many cases in which it is difficult, if not
impossible, to make an unequivocal choice between
the terms basalt and dolerite, since there is not,
and cannot be, any definable line drawn between
them. As field-terms, however, these names
are generally restricted to extrusive and in-
trusive rocks respectively. Many Continental
and American authors use the term diabase in a
sense synonymous with dolerite; whereas in
Britain only altered dolerites are denoted by the
S. Allport : Q.J.G.S., xxx. 1874, p. 520.
J. J. H. Teall : Q.J.G.S., xl, 1884, p. 640.
A. Harker : Mem. Geol. Surv. (Tert. Tg. Rocks Skye), 1904,
Dolomite, de Saussure, 1796. A carbonate rock, con-
sisting predominantly of the mineral dolomite.
Mem. Geol. Surv. S-pec. Re-p. Mineral Resources, vi, 1918,
Dolomite-marble. - - A variety of marble composed
largely of dolomite, due to the metamorphism of
dolomite-rock under physical conditions involving
sufficiently high pressure to inhibit the dissociation
of the compound CaMg(CO.,) 2 .
F. H. Hatch & R. H. Rastall : Q.J.G.S., Ixvi, 1910, p. 507.
84 THE NOMENCLATURE OF PETROLOGY
Dolomitic Limestone. A limestone containing dolo-
mite, but in which CaCO, is dominant over
MgCO v Cf. Magnesian Limestone.
Dolomitisation. -- A general term for the processes
whereby dolomite takes the place of CaCO, in
limestones, the latter thus becoming dolomitic
limestones, or dolomites. The processes are
described as contemporaneous when they take
place shortly after the deposition of the limestone
concerned, and as subsequent when they occur dur-
ing some period later than that during which the
limestones were deposited.
Re-port of the Coral Reef Committee of the Royal Society,
F. Steidtmann : Journ. GeoL, xix, 1911, pp. 223, 392.
R. C. Wallace : Cong. GeoL Inter., C.R., xii (1913), 1914,
F. M. Van Tuyl : GeoL Siirv. loiva, U.S.A., vol. xxv, 1916,
L. M. Parsons : GeoL Mag., 1918, p. 246.
Dome. This term is used not only to connote certain
crystallographic, structural, and geographical
phenomena, but also to describe at least two dif-
ferent types of modes of occurrence of igneous
rocks : It is applied (a) to stocks whose sides
slope away quaquaversally at low and gradually in-
creasing angles beneath the invaded formations ;
and (b) to rounded extrusions of highly viscous
lava squeezed out from a volcano, and congealed
above and around the orifice instead of flowing
away in streams. Portions of older lavas or
ejectamenta may be elevated by the pressure of
the new lava rising from beneath. The second
type of dome is usually distinguished as a volcanic
A. Lacroix : La montagne Pelee et ses eruptions, 1906, p.
no; La montagne Pelee a-pres ses eru-ptions, 1908, p. 31.
S. Powers : Am. Journ. Sci., xlii, 1916, p. 261.
Domite, von Buck. A general term for the hornblende-
and biotite-trachytes of the Puy de Dome. Many
THE NOMENCLATURE OF PETROLOGY 85
of these are olig-oclase-bearing, and the term has
therefore come to be applied more specifically to
olig-oclase-trachytes or trachyandesites.
A. Lacroix : C.R., cxlvii, 1908, p. 830.
Drachenfels Trachyte. A type of trachyte containing
phenocrysts of sanidine and olig-oclase in a ground-
mass of lath-shaped microlites of orthoclase
with sparing- biotite, hornblende, and magnetite.
Dreikanter. A term applied to the three-edged
faceted pebbles formed by wind action in a dry
climate,, whether hot (desert) or cold (glacial).
F. A. Bather : Proc. Geol. Assoc., xvi, 1900, p. 396.
A. Wade : Geol. Mag., 1910, p. 394.
J. W. Evans : Geol. Mag., 1911, p. 334.
J. W. Jackson : Mem. and Proc. Manchester Lit. and Phil
Soc., 1918, Ixii, No. 9.
Druse. - - A cavity whose walls are encrusted with
crystals of the same minerals as those of the en-
closing- rock. To such cavities and the rocks con-
taining* them the term drusy is applied. Cf.
miarolitic. Distinguished from geode by the fact
that the latter can be separated as a hollow nodular
secretion consisting- generally of mineral?; different
from those of the rock in which it occurs.
Dtimalite, T.oeivinson-Lessing, 1905. - - A varietv of
Dungannonite, Adams & Barlow, 1909. A granitoid
igneous rock containing-, in order of abundance,
andesine, corundum, scapolite, micas, and some-
times a little nepheline.
(Dung-annon, Renfrew Co., Ontario.)
F. D. Adams & A. E. Barlow : Geol. Surv. Canada, Mem. 6
(Pub. No. 1082), 1910, p. 322.
Dunite, von Hochstetter, 1864. A peridotite consist-
ing- essentially of olivine, and often containing
J. M. Bell : Geol. Surv. New Zealand, Bull. 12, 1911, p. 31.
Dunsapie Basalt, Bailey, 1910. A type of the Scottish
Carboniferous basalts ; characterised by the pre-
sence of numerous phenocrysts of plagioclase,
86 THE NOMENCLATURE OE PETROLOGY
augite, and olivine, in a normal basaltic ground-
mass. Cf. Lion's Haunch Basalt.
E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), iqio,
G. W. Tyrrell : Trans. Geol. Soc. Glasgow, xiv, 10*2, p. 245.
Dlinstone. (a) A local name for amygdaloidal spilite
or diabase in the neighbourhood of Plymouth.
R. H. Worth : Trans. Devon Assoc., xlviii, iqi6, p. 217.
(b) A local name for certain varieties of magnesian
limestone in the neighbourhood of Matlock..
Durain, Stopes, 1919. A term suggested for the dull,
hard ingredient of bituminous coal, which occurs
in bands or lenticles of variable thickness having a
close, firm, granular texture, generally flecked with
hair-like streaks of bright coal. Under the
microscope durain shows amber- to red-tinted
spores embedded in a dark-grey, nearly opaque
Marie C. Stopes : Proc. Roy. Soc. B., xc, IQIQ, p. 474.
Durbachlte, Sauer. A melanocratic biotite-syenite.
Dyke. An injected wall-like intrusion, cutting across
the bedding or other parallel structures of the in-
vaded formations, and having a thickness narrow
in proportion to its length.
Dynamic Metamorphism. The sum of the processes,
controlled by orogenic movement and differential
stresses, which were sufficiently powerful under the
conditions of temperature at which the changes
took place, to impress a totallv new specific char-
acter on the rocks affected ; involving marked
structural changes due to crushing and shearing at
low temperatures, and extensive recrystallisation
at higher temperatures. The noteworthy features
by which dynamic metamorphism is recognised
become less distinctive at still higher temperatures,
until, when conditions of extensive fusion are ap-
proached, at which point directed pressure be-
THE NOMENCLATURE OF PETROLOGY 87
comes ineffective, they gradually die away. Cf.
P. Quensei : Bull. Geol. Inst. U-psala, xv, 1916, p. 91.
R. A. Daly : Bull. Geol. Soc. Am., 28, 1917, p. 395.
J. J. H. Teall : Proc. Geol. Assoc., xxix, 1918, p. i.
Eclogite, Haiiy. A granulose rock formed of garnet,
pyroxene (omphacite) and sometimes amphibole
(smaragdite), with accessories such as sphene and
zoisite ; probably derived from gabbros, or rocks of
corresponding composition, by high temperature
metamorphism under conditions of high pressure
and differential stress, or from magmas of cor-
responding composition by piezocrystallisation.
T. G. Bonney : Min. Mag., vii, 1886, p. i.
Edolite, Salomon, 1898. A variety of hornfels con-
sisting essentially of felspar and mica. Cordierite-
and andalusite-edolites are recognised. Cf. Avio-
lite and Astite. (Edelo, Italian Alps.)
Effusive. A term applied to igneous rocks poured out
of a vent or fissure, as distinct from those ejected
Ehrwaldite, Pichler, 1875.* A variety of augitite con-
taining both rhombic and monoclinic pyroxenes.
Sjectamenta. A general term for pyroclastic mater-
ials ejected from a volcanic \ent ; classified by
Johnstone-Lavis as essential when they consist of
material directly derived from the magma of the
eruption ; accessory when they consist of re-ejected
portions of the volcanic cone; and accidental
when they consist of older rocks underlying the
H. J. Johaston-Lavis : Proc. Geol. Assoc., ix, 1886, p. 421.
Ejected Blocks. A term applied to the larger frag-
ments of a volcanic breccia, generally derived from
88 THE NOMENCLATURE OF PETROLOGY
the internal or subjacent rocks of a volcano, and
often highly metamorphosed.
H. J. Johnston-Lavis : Trans. Edin. Geol. Soc., vi, 1893,
Ekerite, Brdgger, 1906. An arfvedsonite-granite com-
paratively poor in quartz, containing soda-micro-
cline and microperthite, with arfvedsonite and
aegirine. The rock is normally equigranular, but
passes marginally into ekerite-porphyry.
(Eker, Christiania district.)
Elaterite. A variety of bitumen which, when fresh, is
characterised by being elastic, but which, on expo-
sure, becomes hard and brittle.
Elaeolite-Syenite, Blum, 1861. A synonym for Nephe-
line-syenite, now falling into disuse, except in so
far as it is restricted to comparatively coarsely-
grained types which contain the massive variety of
nepheline distinguished, on account of its greasy
lustre, as elseolite.
Elasticity of Bulk. - - The property possessed by all
substances whereby they tend to recover their ori-
ginal volume after being compressed or extended.
Elasticity Of Form (Rigidity). - - The property pos-
sessed by solid bodies whereby they tend to recover
their original form after being distorted. A per-
fectly rigid body is one which cannot be deformed
by any stress whatever.
Electrostatic Separation. The separation of minerals
according to their electrical conductivity, good con-
ductors, such as ilmenite, being attracted by a
charged body, while bad conductors such as
quartz are unaffected.
T. Crook : Min. Mag., xv, 1909, p. 260; xvi, 1911, p. 109.
Ellipsoidal. A structural term applied to spilitic and
similar rocks which, as a result of the conditions
under which they consolidated, are disposed in a
series of sack- or pillow-like masses. = Pilloiv
J. V. Lewis : Butt. Geol. Soc. Am. y xxv, 1914, p. 595.
THE NOMENCLATURE OF PETROLOGY 89
Elutriation. The process whereby sand or other loose
detritus is separated into grades by cur-
rents of water of known and controlled velocity.
Using upward-moving currents of water at 15 C.
a velocity of 6.7 m.m. per second suffices to separ-
ate silt from sand, and one of 0.12 m.m. per second,
mud from silt.
T. Crook : In Sedimentary Rocks (Hatch & Rastall), Lon-
don, 1913, p. 349.
P. G. H. Boswell : British Resources of Refractory Sands,
London, 1918, p. 20.
Eluvium. A general term, used more particularly by
Continental and American writers, for residual
Elvan. A Cornish name (el = rock ; van = white,
Keltic) sometimes systematised as elvanite, for
quartz-porphyry and other dyke rocks of similar
composition. The term Blue Elvan is applied to
Emery-rock. A granulose rock consisting essentially
of corundum and iron-ores, which may be formed
by magmatic segregation or by the metamorphism
of laterite. The term emery, alone, connotes the
commercial product obtained by crushing the rock.
G. S. Rogers : Ann. New York Acad. Sci., xxi, 1911, p. 66.
H. Miiller : Zeit. f. Prakt. Geol., xxiv, 1916, p. u.
Enantiotropic. A term applied to the transition of
one polymorphic form of a substance to another
(e.g., quartz^=r>tridymite) when the change can
take place in either direction according to the con-
Enclaves, Lacroix, 1893. - - A general term for en-
closures or inclusions of any kind contained in
igneous rocks. The types recognised by Lacroix
are set forth in the following four paragraphs.
A. Lacroix : Les Enclaves des Roches volcamques, Paris,
1893, p. 8 ; La Montagne Pelee et ses Eru-ptions, 1904, p.
y o THE NOMENCLATURE OF PETROLOGY
Enclaves Enallogenes. Xenoliths or accidental in-
Enclaves HomoeOgeneS. Autoliths or cognate in-
clusions- formed from the same magma as the
enclosing rock. They are respectively described as
(a) synmorphes (synmorphous), when they have the
same textures as the enclosing rocks ; (b) plesio-
morphes, when they have similar but not identical
textures ; and (c) allomorphes, when the textures
are notably different from those of the enclosing
rocks. These types in turn may be homologues,
when the composition of enclave and enclosing rock
is the same, or antilogues, when the compositions
are different, that of the enclave being always the
Enclaves Pneumatogenes. -- Enclaves formed at
great depths by the action of the volatile fluxes of
A. Lacroix : Bull. Soc. franf. Min., xxiv, 1901, p. 488.
Enclaves PolygeneS. Enclaves formed by the action
of the magma or its volatile fluxes on another type
Enclosures. -- A term applied to allothigenous frag-
ments of rocks or minerals included in igneous
rocks ; generally referred to as inclusions.
S. Powers : Journ. Geol., xxiii, 1915, pp. i and 166.
Endogenetic. A term applied to geological processes
originating within the earth, and to rocks, ore-
deposits, and land-forms which owe their origin to
such processes. Contrasted with Exogenetic.
T. Crook : Min. Mag., xvii, 1914, p. 72.
Endogenous Enclosures. = Cognate Inclusions.
Endomorphism, Fournet, 1867. - The modification
produced in an igneous rock due to the partial or
complete absorption (assimilation) of portions of
the rocks invaded by its magma ; a phase of con-
tact-metamorphism in which attention is directed
to the changes suffered by the intrusion instead of
to those produced in the invaded formations.
THE NOMENCLATURE OF PETROLOGY 91
Enrichment. - - The sum of the secondary processes
whereby one part of an ore-deposit is enriched at
the expense of the parts above.
W. H. Emmons : U.S.G.S. Bull., 625, 1917.
Eo-, Nordenskiold, 1893. - - A prefix indicating the
alteration of volcanic rocks bv devitrification or re-
crystallisation ; e.g., Eorhylite, eoandesite, etc.
O. Nordenskiold : Bull. Gebl. Inst. U-psala^ i, 1893, p. 153.
Eozoon. - - The generic name of a supposed foramini-
feral fossil occurring in the Grenville Limestone ;
now known to be an inorganic aggregate of pairs
of minerals such as calcite and serpentine.
H. J. Johnson-Lavis & J. W. Gregory: Sci. Trans. Roy.
Dublin Soc., v, 1894, p. 259.
Epi-, Giimbel, 1888. A prefix, indicating alteration,
properly used as a qualifier to the names of rocks
which have suffered a change in mineral composi-
tion, but wrongly used in epidiorite, where it is
added to the name of a rock (diorite) analogous in
mineral composition to that of another rock
(dolerite) as modified by alteration. The following
terms are thus synonymous or nearly so- -epidiorite
(Giimbel), epidiabase (Issel), epidolerite, and apodo-
lerite (Van Rise).
Epi-, Grubenmann, 1907. A prefix used as a qualifier
to the group-names suggested by Grubenmann for
metamorphic rocks, to indicate that the type so dis-
tinguished belongs to the " upper zone " of meta-
morphism. In this zone the distinctive physical
conditions are moderate temperature, lower hydro-
static pressure and powerful stress, and the rocks
characteristically produced include mylonites, and
cataclastic rocks generally, phyllites, chlorite-
schists, talc-schists, porphyroids, and in part
marbles and quartzites. Cf. Meso- and Kata-.
U. Grubenmann : Die Kristallinen Schifer, II, 1907, pp.
9 2 THE NOMENCLATURE OF PETROLOGY
EpiclastlC, Teall, 1887. -- A term applied to clastic
rocks formed by exogenetic processes, i.e., to detri-
tal sediments formed at the surface of the earth.
Epidiabase, Issel, 1892. A term proposed in place of
et>idiorite in order to avoid confusion with the term
diorite. British writers, however, have continued
to use the older term, denned below.
Epidiorite. Gunibel, 1874. A doleritic or basaltic rock
in which the augite has suffered alteration to horn-
blende, so that the rock approaches the composi-
tion of a diorite. Distinguished from cliabasc by
the less extreme alteration of the felspars.
J. S. Flett : Men?. GeoL Surv., 359 (Lizard), 1912, p. 102.
Epidosite, Reichenbach, 1834. - - A term applied to
altered igneous rocks, or veins traversing- them,
essentially containing- epidote and quartz, and
generally other secondary minerals such as uralite
J. S. Flett : Mem. GeoL Surv. (Lizard), 1912, p. 50.
F. L. Stillwell : Aust. Ant. Ex-p. Sci. Re-p. A, iii I (i) (Met.
Rocks, Adelie Land), 1918, p. 58.
Epigene. A. Geikie, 1879. A general term for geolo-
gical processes originating at or near the surface
of the earth. By Judd the term was later adopted
as a group name for volcanic and sedimentary
classes of rocks. Cf. Plypogene ; Exogenetic.
Epigenetic. A term now generally applied to ore-de-
posits of later origin than the rocks among which
they occur ; contrasting them with those that are
contemporaneous with the enclosing rocks (syn-
Equigranular. A term applied to the texture of rocks
whose essential minerals are all of one order of size.
Equilibrium. - - The state of a system when all the
operative forces so balance each other that the sys-
tem would continue to remain in the same state
indefinitely, provided no change were made in tem-
perature, pressure, or composition.
THE NOMENCLATURE OF PETROLOGY 93
Erosion. The action of various mechanical agents in
wearing- down the land ; generally restricted to pro-
cesses acting by lateral rather than by vertical ex-
cavation, those in which the latter action predomi-
nates being- distinguished under the term
Espichellite, Souza-Brandao, 1907- A mafic dyke-
rock containing phenocrysts of olivine and
hornblende with smaller ones of pyroxene, mag-
netite and pyrite, in a groundmass composed of
various mafic minerals, orthoclase-mantled labra-
dorite, and alteration products such as calcite,
chlorite, serpentine, and analcite.
(C. Espichel, near Lisbon.)
V. Souza - Brandao : Ann. Acad. Polytech. do Porto
(Coimbra), 1907, ii, p. 30.
Essential. A term applied to minerals whose presence
in a rock helps to decide the choice of specific
name given to the rock, and whose recognition is
thus a necessary preliminary to the diagnosis of
the rock. An essential constituent is not neces-
sarily a major constituent, for the presence in a
rock of quite small amounts of such minerals as
nepheline, olivine, or quartz, may radically affect
its classification ; these minerals are therefore
always essential, unless merely local traces are
Essexite, Sears, 1891. A phanerocrystalline igneous
rock regarded as an alkali variety of gabbro, con-
taining green and purple pyroxenes and plagio-
clase (andesine to bytownite) with or without soda-
amphiboles and olivine. Among the felsic minerals
nepheline or analcite may occur in small amounts,
and orthoclase or soda-orthoclase is always
developed. By decrease in potash-felspar and
increase of the felspathoid minerals the type passes
into therdlite. (Essex Co., Mass.)
A. Scott : Geol. Mag., 1915, pp. 455 and 513.
A. Lacroix : C .R,, clxx, 1920, p. 20.
94 THE NOMENCLATURE OE PETROLOGY
Esterellite, Michel Levy, 1897. A holocrystalline
variety of dacite or quartz-microdiorite, containing-
phenocrysts of quartz, zoned andcsine, and horn-
blende. (Esterel, France.)
A. Michel Levy : Bull. Surv. Carte. Geol. France, ix. No.
57, 1897, p. 19
Ethmolith, Salomon, 1903. An injected transgressive
igneous intrusion, having- the form of an irreg-ular
funnel. The only example described is that of the
W. Salomon : Sitz K. -preuss. Akad. Wiss., -phys-math.
Classe, xiv, 1903, p. 310.
Elicrite, Rose, 1835. A variety of gabbro formed es-
sentially of bytownite-anorthite and augite. The
term has also been applied to meteorites of a simi-
lar mineral composition.
A. Harfcer : Mem. Geol. Surv. Scot.. 60 (Small Islejs), 1908.
Eugranitic Texture, Brogger. See Granitic.
Euhedral, Pirsson, 1896. See Idiomorphic.
Euktolite, Rosenbusch, 1899. See Venanzite.
Eulysite, Erdmann, 1849. A granulose \-ariety of py-
roxene-peridotite containing- mang-aniferous faya-
lite and g-arnet and abundant magnetite.
]. Palmgren : Bull. Geol. Inst. U-psala, xiv, 1915, p. 109.
Euphollte, Cordier, 1868. - - A variety of euphotide
characterised by the presence of talc.
Euphotide, Hatiy, 1822. A term orig-inallv svnony-
mous with gabbro, and referring- to the reflection of
lififht bv the green diallag-e present. The rock to
which the name was first applied was afterwards
found to have suffered saussuritisation, and con-
sequently the term is now applied to g-abbros
whose felspars have been altered in that way.
T. G. Bonney : Phil. Mag., xxxiii, 1892, p. 237.
Eurite, D'Aubuisson, 1819. A g-eneral term applied
to compact felsitic rocks without phenocrysts, hav-
THE NOMENCLATURE OF PETROLOGY 95
ing the composition of quartz-porphyry or por-
phyry. The term has also been used in an ex-
tended sense to cover all aphanitic rocks of grani-
tic composition whether porphyritic or not.
G. A. J. Cole & A. V. Jennings : Q.J.G.S., xlv, 1889, p. 426.
Eutaxic, Keyes, 1901. - - A general term applied to
stratified ore-deposits, as opposed to those that
are unstratified, or ataxic.
C. R. Keyes : Trans. Amer. Inst. Min. Eng., xxx, 1901, p.
3 2 3-
Eutaxitic Structure. A term describing the streaked
or blotched appearance of certain volcanic rocks
due to the alternation of bands or elongated lenses
of different colour, composition or texture ; the
bands, etc., having been originally ejected as in-
dividual portions of magma which were drawn out
together in a viscous state and formed a hetero-
geneous mass by welding. Cf. Flow-breccia.
Eutectic Mixture. -- A discrete mixture (not a com-
pound) of two or more minerals which have cry-
stallised simultaneously from the mutual solution
of their constituents, the two or more minerals
being in definite proportions. Simultaneous cry-
stallisation sometimes gives rise to graphic texture,
but it does not necessarily do so, as the develop-
ment of graphic intergrowth involves other factors
besides eutectic proportions.
A. L. Day : Bull. Geol. Soc. Am., xxi, 1910, p. 147.
Eutectic Point. The lowest temperature, at any given
pressure, at which the constituents of two (or
more) minerals can exist together in a liquid state
of mutual solution, and at which the two (or more)
minerals can crystallise simultaneously in a
constant proportion to each other by weight.
Eutectic Ratio. The ratio by weight of two minerals
which crystallise at the eutectic point simultan-
eously from the mutual solution of their consti-
9 b THE NOMENCLATURE OF PETROLOGY
Evergreenite, Ritter, 1908. A variety of nordmarkite
characterised by the presence of sulphide-ores (chal-
copyrite and bornite).
(Evergreen Mine, Colorado.)
E. A. Ritter : Trans. Am. Inst. Min. Eng., xxxviii, 1908,
p. 751; U.S.G.S. Prof. Paf., 94, 1917, p. 127.
Exogenetic. A term applied to geological processes
originating at or near the surface of the earth (e.g.,
denudation and deposition), and to rocks, ore-de-
posits, and land forms which owe their origin to
such processes ; contrasted with Endogenetic.
T. Crook : Min. Mag., xvii, 1914, p. 72.
Exogenous Enclosures. = Accidental inclusions, =
xenoliths and xenocrysts. See Enclaves.
Exomorphism, Fournet, 1867. The modification pro-
duced in the invaded rocks by intrusions which
traverse them ; = Contact metamorphism in the
usual sense, as opposed to endomorphism.
Explosion-tuffs, Green, 1919. Tuffs of which the con-
stituents have been dropped directly into place after
being ejected from a volcanic vent, the term thus
distinguishing such tuffs from the more ordinary
types which are washed into place.
J. F. N. Green : Proc. Geol. Assoc., xxx, 1919, p. 155.
Fabric, C.I.P.W., 1902. A term suggested for that
part of a texture which depends on the shapes and
arrangement of the constituents of a rock ; texture
being considered as a function of crysLallinity,
granularity, and fabric.
Facies. A term denoting " the sum of the lithological
and palseontological characters exhibited by a
deposit " regarded as criteria of the conditions
which controlled their formation (e.g., alluvial,
glacial, littoral facies, etc.). Also applied to
varieties of a single body of igneous rock which
THE NOMENCLATURE OF PETROLOGY 97
differ in structure or composition from the normal
rock-type of the mass.
Fahlbaild. -- A Scandinavian mining- term for meta-
morphic rocks heavily impregnated with iron-ores
or sulphide minerals.
Fakes. A vernacular term for platy formations such
as micaceous flagstones associated with oil-shales
False-cleavage, Marker, 1885. -- See Strain-slip-
A. Harker : Rep. Brit. Assoc. (1885), 1886, p. 836.
Fanglomerate, Laws on f 1913. A term proposed for
the coarser deposits occurring in the upper parts
of alluvial fans.
A. C. Lawson : Bull. Dept. Geol. Univ. California, vii, No.
1 5> I 9 1 3> P- 3 2 9-
Farrisite, Brogger, 1898. -- An aphanitic dyke rock
containing barkevikite and diopside as its chief
mafic minerals, with lepidomelane, olivine and
magnetite in smaller quantities, the felsic minerals
felspar and nepheline, being almost entirely altered
to, or replaced by zeolites.
(Farris See, Christiania District.)
W. C. Brogger : Eruptivgest. Kristiania, iii, 1898, p. 64.
Fasibitikite, Lacroix, 1915. A mesocratic variety of
riebeckite-cegirine-gpranite containing eucolite and
zircon. (Ampasibitika, Madagascar.)
A. Lacroix : C.R., clxi, 1915, p. 253.
A Holmes : Geol. Mag., 1915, p. 267.
Fasinite, Lacroix, 1916. A phanerocrystalline rock
composed essentially of augite and nepheline, with
subsidiary olivine, biotite, etc. The type is
chemically equivalent to berondrite, and differs
from bekinkinite by the absence of hornblende and
A. Lacroix: C.R., clxiii, 1916, p. 257; clxx, 1920, p. 20.
Felsic, C.I.P.W., 1912. A mnemonic term (recalling
felspar, /eZspathoid and silica) for felspathic mine-
rals and quartz actually present in an igneous
98 THE NOMENCLATURE OF PETROLOGY
rock, and also for rocks largely composed of such
minerals; not synonymous with salic which refers
to the normative compounds of a rock calculated
from its analysis.
C.I.P.W. : Journ. Geol., xx, 1912, p. 561.
Felsite. An igneous rock with or* without phenocrysts,
in which either the whole or the groundmass con-
sists of cryptocrystalline aggregates of felsic
minerals, quartz and orthoclase being those char-
acteristically developed. When phenocrysts of
quartz are present the rock is termed Quartz-fel-
site or Quartz-porphyry, the latter term being now
more customary than the former.
Felsitic. A term applied to the cryptocrystalline tex-
ture seen in the groundmass of quartz-felsites and
similar rocks ; and which may be original as the
result of a rapid cooling of a viscous magma, or
secondary, as the result of the devitrification of a
natural glass. By many authors this texture is
described as micro/ els itic, the term felsitic alone re-
ferring only to the aphanitic appearance of a hand
specimen. The latter, examined in thin section,
may then be micro granitic, micro graphic, ortho-
phyric, micropoikilitic, or microfelsitic, etc.
Felsophyre, Vogelsang, 1867. -- A general term for
porphyries and quartz-porphyries having a felsitic
or cryptocrystalline groundmass.
Felspathic-tawite. A phanerocrystalline rock, inter-
mediate in composition between taivite and soda-
lite-syenite composed essentially of sodalite and
alkali-felspar (the former being predominant) with
J. J. O'Neill : Geol. Surv. Canada Mem., 43 (Pub. Xo.
1,311), 1914, p. 46.
Femic, C.I.P.W., 1902. A mnemonic term (recalling
/errowagnesian) for the group of standard norma-
tive minerals, in which the pyroxene and olivine
molecules and most of those of the accessory
minerals appear. The corresponding term for the
THE NOMENCLATURE OF PETROLOGY 99
ferromagnesian minerals actually present in a rock
FergUSite. A variety of shonkinite or melanocratic
nepheline-syenite, containing- orthoclase-nepheline
pseudomorphs after leucite.
(Fergus Co., Montana.)
L. V. Pirsson : U.S.G.S., Bull. 237, 1905, p. 83.
Ferricrete, Lamplugh, 1902. A term suggested for
conglomerates formed by the cementation of
gravels by the oxidation of percolating solutions
of iron salts.
G. W. Lamplugh : Geol. Mag., 1902, p. 575.
Ferrite, Vogelsang, 1872. A general non-committal
descriptive term for reddish-brown amorphous
alteration products which are presumably ferru-
ginous, but which cannot be definitely diagnosed by
ordinary optical methods.
Ferrolite, Wads-worth, 1891. -- A general term pro-
posed for iron-ore rocks.
Fireclay. A general term for refractory clays which
resist exposure to high temperatures without dis-
integrating or becoming soft and pasty by melting.
Such clays are abundant beneath the coal seams
of the Coal Measures, and are characterised
chemically by a low content of alkalies and lime.
W. M. Hutchings : Geol. Mag., 1891, p. 164.
J. W. Gregory : Proc. Roy. Soc. Edin., xxx, 191, p. 348.
A. H. Cox : Geol. Mag., 1918, p. 56.
Flaser-gabbro. - - A term for dynamically meta-
morphosed gabbro which has been crushed and
sheared into lenticular masses separated by wavy
ribbons and streaks of finely granulated and recry-
(stallised material. The phacoidal relics of the
original rock have not lost their igneous character,
and the rock as a whole has not become a schist.
J. S. Flett : Mem. Geol. Surv., 359 (Lfzard), 1912, p. 87.
neiss. A general term for dynamically meta-
morphosegj rocks, usually igneous, which, like the
flaser-gabbro defined above, still contain coarse-
ioo THE NOMENCLATURE OF PETROLOGY
grained lenticular masses or phacoids of parts of
the original rock in a finely crystalline foliated
Fleckschiefer. See Spotted Slates.
Flint. A more or less pure siliceous rock composed
mainly of granular chalcedony together with a
small proportion of opaline silica, and occurring
in nodules, irregular concretions, layers, and vein-
like masses in the Chalk. The fracture is conchoi-
dal, whereas in chert a splintery fracture is more
W. Hill : Proc. Geol. Assoc., xxii, 1911, p. 61.
G. A. J. Cole : Geol. Mag., 1917, p. 64.
W. A. Richardson : Geol. Mag., 1919, p. 535.
Flinty Crush-rock, Clough. A black flinty product of
dynamic metamorphism associated with mylonite,
and representing a fritted or partly fused variety of
the latter ; generally structureless, but occasionally
showing incipient traces of crystallisation.
Mem. Geol. Surv. (N.W. Highlands), 1907, pp. 124, 221, 249.
S. J. Shand : Q.J.G.S., Ixxii, 1916, p. 209.
Flowage. A term, applied to the deformation of rocks,
stressed beyond the limit of elastic recovery, by
plasticity (molecular flow), granulation (closely-
spaced fracturing), gliding (on cleavage planes),
J. Barrell : Journ. Geol., xxiii, 1915, p. 427.
Flow-breccia. - - A term describing lavas in which
fragments of partly solidified magma, produced by
explosion or flowage, have become welded together
or cemented by the still fluid parts of the same
Flow Structure. A structure, generally, but not ne-
cessarily, restricted to volcanic rocks, in which the
stream lines of the magma are revealed by alter-
nating bands of differing composition, crystallinity
or texture, or by a sub-parallel arrangement of
prismatic or tabular crystals.
THE NOMENCLATURE OF PETROLpGV 101
Fluxion Gneiss, Gregory, 1894. A gneis&ose or band-
ed igneous rock with a fluxion structure due to the
movements of a viscous magma during the later
stages of crystallisation. Cf. Primary foliation.
Fluxion Structure. A structure of igneous rocks due
to the movement involved in intrusion or to con-
vection, and evidenced by the parallel or sub-paral-
lel disposition of adjacent phenocrysts, or by the
alternation of mineralogically unlike layers. The
latter type of structure is generally distinguished
F. F. Grout : fourn. Geol., xxvi, 1918, p. 439.
Foliation, Darwin, 1846. A structure represented
most characteristically in schists, due to the
parallel disposition in layers or lines of one or more
of the conspicuous minerals of the rock, the
parallelism not being a direct consequence of
stratification. The layers may be plane lamellae,
gently undulating or strongly crumpled, or they
may be lenticular or phacoidal. Foliation may be
described as closed when the minerals to which the
structure is due form a megascopically felted aggre-
gate, and as open when the controlling minerals are
megascopically discontinuous or in disconnected
T. G. Bonney : Geol. Mag., 1919, p. 196.
Foliate, Bastin, 1909. A general term for any foliated
Forellenstein, ^. Rath. = Oss y pite = Troctolite.
Formation. A term applied stratigraphically to a set
of strata possessing a- common suite of lithological
and /or faunal characteristics.
Fortunite, de Yarza, 1896. A variety of verite com-
posed of phenocrysts of olivine and phlogopite in
a brown glass containing small crystals of py-
roxenes, biotite and orthoclase. (Fortuna, Spain.)
A. Osann : Festschrift H. Rosenbusch, Stuttgart, 1906, p.
.102 THE NOMENCLATURE OF PETROLOGY
Fourchite, Williams, 1890. An olivine-free monchi-
quite characterised by an abundance of titanaugite.
(Fourch Mts., Montana.)
J. F. Williams : Geol. Surv. Arkansas Ann. Rep., ii, 1890,
Foyaite, Blum, 1861. A nepheline-syenite consisting
of perthitic-orthoclase, microline, and nephe-
line, with soda-pyroxenes and/or amphiboles. By
Roseribusch the term is applied to all varieties of
nepheline-syenite which contain dominantly potash
felspars, and this is the common usage of the
term. Brdgger, however, has caused a certain
confusion in its use by giving the term a textural
significance, all nepheline-syenites with a trachy-
toid texture being joyaite according to his defini-
tion. (Foya, Serra de Monchique, Portugal.)
Fruchtschiefer. See Spotted Slates.
Fulgurite, Arago f 1821. A glassy and often tube-like
mass produced by the action of lightning on loose
or compact rocks.
A. A. Julian : Journ. Geol., ix, 1901, p. 673.
Fuller's Earth. A very fine-grained deposit consisting
chemically mainly of hydrated aluminium silicate,
but differing from ordinary clay in its unusually
low plasticity. It is used for degreasing wool and
for clarifying oil. (Cotteswolds, and Surrey.)
C. L. Parsons : V .S. Bureau of Mines, Bull. 71, 1913, p. 6.
G. M. Davies : Proc. and Trans. Cray don Nat. Hist, and
Sci. Soc., 1915-16, pp. 63, 92.
Fusain, Stevenson, 1911. A term suggested to replace
" mother of coal " and " mineral charcoal " ; i.e.,
for an ingredient of bituminous coal which con-
sists of fibrous strands forming patches and wedges
somewhat flattened parallel to the bedding plane.
In thin section fusain appears black and nearly
opaque, but may show the cellular structure of
Marie C. Stopes : Proc. Roy. Soc. B., xc, 1919, pp. 472-4,
THE NOMENCLATURE OF PETROLOGY 103
Fusion Point. The temperature at which a crystalline
substance undergoes a discontinuous change from
the solid to the liquid state, absorbing latent heat
while the change is effected. The term has no
precise meaning as applied to materials such as
glass, or rocks composed of more than one mineral.
A. Plarker : Nat. Hist. Ig. Rocks, 1909, p. 153.
A. L. Day : Fort, der Min. Krist. Pet., iv, 1914, p. 189.
Gabbro, von Buck, 1810. A phanerocrystalline rock
consisting of labradorite, or bytownite, and augite
(generally diallage). With the incoming of olivine
the rock becomes Olivine- gabbro. If the plagio-
clase be anorthite, the term Eucrite may be used.
W. S. Bayley : Journ. Geol., i, 1893, p. 433.
J. W. Sollas : Trans. Roy. Irish A cad., xxx, 1894, p. 477
A. Harker : Q.J.G.S., 1, 1894, p. 311 (Carrock Fell).
Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904, p. 102,
Mem. Geol. Surv. Scot., 60 (Small Isles), 1908, p. 93.
J. S. Flett : Mem. Geol. Surv., 359 (Lizard), 1912, p. 81.
M. N. Nebel : Econ. Geol., xiv, 1919, p. 367 (Duluth).
H. C. Cooke : Geol. S:trv. Canada Mus. Bull. 30, 1919
Gabbro-Syenite, Tarassenko, 1895. A descriptive
name for rocks now known as monzonite, in which
the plagioclase is at least as calcic as labradorite.
= Orthoclase-gabbro. Cf. Granogabbro
Gallaston Basalt, Hatch, 1892. A type of the Scottish
Carboniferous basalts, intermediate between the
Jedburgh and Dalmeny types ; characterised by
abundant small phenocrysts of olivine relative to
those of plagioclase, in an ophitic groundmass.
F. H. Hatch : Q.J.G.S., xlviii. 1892, p. 129.
Gangue. -- A general term for the non-metalliferous
mineral aggregates associated with ores in mineral
io 4 THE NOMENCLATURE OE PETROLOGY
Canister. A compact, highly siliceous sedimentary
rock, with a fine and even granular texture ; com-
posed of medium to fine grains of angular quartz
cemented with silica.
Mem. Geol. Surv. S-pec. Rep. Mineral Resources of Great Bri-
tain, vi, 1918, p. 3.
Garbenschiefer. See Spotted Slates.
Garwaite, Duparc cV Pearce, 1904. -- A variety of
peridotite-porphyrv containing phenocrysts of
diopside in a micro-granular groundmass com-
posed of pyroxene, olivine, magnetite, and
chromite. (Tilai Range, N. Urals.)
L. Duparc & F. Pearoe : C.R., cxxxix, 1904, p. 154.
Garganite. Viola &> de Stefani, 1893. A variety of
vogesite containing both augite and hornblende.
Gauteite, Hibsch, 1897. A variety of rrachyandesite
occurring as dykes ; a bostonite-like rock with
micro-phenocrysts of andesine. (Gaute, Bohemia.)
Gebtirite-dacite, Gregory, 1901. -- A holocrystalline
variety of dacite occurring as a dyke rock, and
characterised by the presence of hypersthene.
J. W. Gregory : Proc. Roy. Soc. Victoria, xiv, 1902, p. 193.
Gel. A colloidal aggregate composed of two phases,
as in a jelly ; one phase forming a continuous
framework enclosing cells occupied by another
Generation. A term applied to each of two or more
groups of crystals of the same mineral in igneous
rocks, when the sizes of the crvstals in the different
groups are conspicuously different. Thus, if pheno-
crysts of orthoclase are embedded in a groundmass/
containing crystals of orthoclase, the former are
said to belong to an earlier generation than the
latter, and the two groups are considered to in-
dicate different periods of formation corresponding
to changes in the cooling conditions.
Geode. A hollow secretion or concretion, lined with
crystals on the inside walls, and separable as a
THE NOMENCLATURE OE PETROLOGY 105
discrete nodule from the rock (usually argillaceous
or calcareous) in which it occurs. Cf. Druse.
R. S. Bassler : Proc. U.S. Nat. Museum, xxxv, iqo8, p. 133.
F. M. Van Tuyl : Am. Jo^^rn. Sci. } xlii, igi6, p. 34.
Geological Thermometer. A term applied to known
temperature limits within which certain minerals
or mineral aggregates must have formed ; based
on the thermal data relating to the fusion-points of
rocks and minerals, and the inversion- or transi-
tion-points of allotropic modifications of rock-
forming- compounds, and in general to the equili-
brium conditions and stability ranges under dif-
ferent conditions of pressure for various minerals,
allotropes, solid-solutions, eutectics, and other
F. E. Wright & E. P. Larsen : Am. Journ. Sci., xxvii, 1909,
A. L. Day : Bull. Geol. Soc. Am., xxi, 1910, p. 176.
Geyserite. A general term for the siliceous deposits,
usually opaline, formed around thermal springs
and geysers, whether loose, compact, or con-
Ghizite, Washington, 1914. A variety of analcite-
basalt characterised by the presence of biotite.
(Mt. Ferru, Sardinia.)
H. S. Washington : Journ. Geol., xxii, 1914, p. 748.
Gibelite, Washington, 1913. A variety of alkali-
trachyte, containing- soda-microcline, with small
amounts of colourless to green augite and dark-
brown hornblende. (Pantelleria.)
H. S. Washington : Journ. Geol., xxi, 1913, p. 684-91.
Gieseckite-porphyry. An altered nepheline-porphyry
in which porphyritic crystals of nepheline are re-
placed by s.caly sericitic aggregates. =Liebenerite-
Gilsonite. See Uintaite.
Giumarrite, Viola, 1901. -- A variety of amphibole-
monchiquite. (Giumarra, Sicily.)
io6 THE NOMENCLATURE OF PETROLOGY
Gladkaite, Duparc &> Pearce, 1905. A quartz-lam-
prophyre containing- andesine and hornblende,
and in smaller quantities both micas and epidote =
quartz spessartite. (Gladkaia Sopka, N. Urals.)
L. Duparc & F. Pearce : Mem. Soc. de Phys. e t tfHist.
Nat. Geneva, xxxviii, 2, 1914, p. 136.
Glass. A general term for the amorphous consolida-
tion products of mag-mas, whether forming- the
whole of a rock, as in obsidian or pumice, or only
a groundmass or mesostasis. Glass natural or
artificial is described physically as a rigid solution
to distinguish it from solid solutions which are
N. L. Bowen : Journ. Wash. Acad. Sci, viii, jqi8, p. 88.
G. V. Wilson : Journ. Soc. Glass Tech., ii, 1918, p. 177.
GlailCOphane-SChist, Barrois, 1883. A well-marked
type of amphibole-schist, in which glaucophane in-
stead of hornblende is an abundant mineral.
Epidote is frequently present, and quartz and mica
varieties are recognised.
H. S. Washington : Am. Journ. Sci., xi, IQOI, p. 35.
E. Murgoci : Bull. De-pt. GeoL Univ. California, iv, 1906,
Globigerina Ooze, Ehrenberg^ cV Bailey, 1853. A
widespread deep-sea deposit largely composed of
the shells of foraminifera, among which Globigerina
is especially abundant. Other calcareous remains
are present (about 10 per cent.), together with an
inorganic residue (about 3 or 4 per cent.) having
the composition of red clay (q-v.).
J. Murray & A. F. Renard : " Challenger " Re-h. (Deep Sea
Deposits), 1891, p. 213.
Globosphaerite, Vogelsang, 1872. See Globulite
Globulite, Vogelsang, 1872. - - An extremely minute
sphere-like crystallite, i.e., having no reaction on
polarised light. When loosely aggregated into
irregular cloudy masses, the latter are known as
ciimulites, while more closely aggregated masses
THE NOMENCLATURE OF PETROLOGY 107
are called globosph&rites. Linear strings of
globulites are known as margantes.
F. Rutley : Min. Mag., ix, 1891, p. 261.
Glomeroplasmatic, Lcewinson-Lessing, 1900. A term
applied to the texture of granites or gneissose rocks
in which the individuals of a certain mineral (such
as biotite) are locally concentrated into conspicuous
open clusters, and not into closed groups as in
A. Holmes : Q.J.G.S., Ixxiv, 1918, p. 55.
Gfomeroporphyritic, ]udd, 1886. A texture produced
by the; segregation of numerous crystals of the
same mineral into compact and conspicuous groups
which give the rock a porphyritic aspect.
J. W. Judd : Q.J.G.S., xlii, 1886, p. 71.
Gneiss. A foliated or banded phanerocrystalline rock
(generally, but not necessarily, felspathic and of
granitic or dioritic composition) in which granular
minerals, or lenticles and bands in which they pre-
dominate, alternate with schistose minerals, or
lenticles and bands in which they predominate.
The foliation of gneiss is more " open," irregular,
or discontinuous than that of schist (q-v.).
J. J. Sederholm : Bull. Comm. Geol. FinLande, No. 23,
1907, p. 91.
A. G. Hogbom : Bull. Geol. Inst. U-psala, x, 1910, p. 29.
J. D. Trueman : Journ. Geol., xx, 1912, p. 236.
J. S. Flett : Mem. Geol. Surv. (Lizard), 1912, pp. 55 and 119.
J. J. H. Teall : Mem. Geol. Surv. (i\.W. Highlands), 1907,
A. Holmes : Q.J.G.S., Ixxiv, 1917, p. 52.
Gneissose Granite. A general term for granitic rocks
twith gneissose structure due, not to meta-
morphism, but to the constrained movements of a
viscous magma during crystallisation = Granite-
gneiss = Primary igneous gneiss.
G. Barrow : Q.J.G.S., xlix, 1893, p. 330.
Gneissose Structure. - - The structure of phanero-
crystalline rocks, having an open foliation, and in-
termediate in character between schistose rocks
with a closed foliation and granulose rocks
io8 THE NOMENCLATURE OF PETROLOGY
with no foliation. Lamellar or prismatic minerals
may be distributed in parallel planes or lines
through the more granular body of the rock, or
bands and lenticles of granular minerals may alter-
nate with folise of lamellar minerals.
Gondite, Fermor, 1909. -- A spessartite-quartz rock,
probably produced by the metamorphism of man-
ganiferous sediments, and named after the Gonds
of the Central Provinces of India, where the
Gondite Series occurs.
L. L. Fermor : Mem. Geol. Surv. India, xxxvii, 1909, p. 306.
Gondite Series, Fermor, 1909. - - A series of man-
ganiferous rnetamorphic rocks belonging to the
Dharwar System of India, and characterised by
the presence of spessartite, rhodonite, and quartz.
Gossan. A term applied to the weathered or other-
wise decomposed upper zone of a lode, char-
acterised by an abundance of oxidised and
hydrated alteration products such as limonite.
Grade. A term applied to those grains of any detrital
sediment which are of the same order of size, the
latter being conventionally determined by a range
of diameters. In the mechanical analysis of
sands, etc., the relative proportion of each grade
is determined. The following classification of
grade-sizes is used for this purpose :
Name / Grade . Range of Diameters .
Pebbles ... ... ... ... ... Greater thanio mm.
Gravel ... ... 10 mm. _ 2 mm.
very coarse sand... ... ... 2 mm. - i mm.
coarse sand i mm. - 0.5 mm.
medium sand 0.5 mm. -0.25 mm.
fine sand 0.25 mm. - o.i mm.
( superfine sand } o.i mm. -0.05 mm.
o.,, I coarse silt J
( silt ... ... ... ... 0.05 mm.~o.oi mm.
Mud or clay ... ... ... ... Less than o.oi mm
S. Oden : Proc. Roy. Soc. Edin., xxxvi, 1915-16, p. 219.
P. G. H. Bos well : British Resources of Sands and Rocks
used in Glass Making, and Ed., 1918, p. 13.
A. Holmes : The Physical and Geological Characters of
Concrete Aggregates, B.F.P.C. " Red Book," 256, 1920.
THE NOMENCLATURE OF PETROLOGY 109
Graded Sediments. - - A general term for loose or
cemented detrital sediments in which the allogenic
grains lie mainly within the limits of a single
P. G. H. Boswell : Sands and Rocks used in Glass Making,
Grahamite. (1) A type of meteorite belonging to the
Me so side rite group ; (2) a variety of asphalt or
asphaltite having a specific gravity of 1.15, and
soluble in carbon disulphide.
G. H. Eldridge : U.S.G.S., 22nd Ann. Re$., Pt. i, 1901,
Granite. A phanerocrystalline rock, consisting
essentially 01 quartz and alkali-felspars with any
of the following : biotite, muscovite, and amphi-
boles and pyroxenes (including soda varieties in
the alkali- granites). By increase of oligoclase or
andesine relative to> the alkali-felspars, granite
passes through adamellite (quartz-monzonite) to
granodiorite and quartz-diorite (tonalite). By
decrease of quartz, granite passes through quartz-
syenite into syenite.
A. Marker & J. E. Marr : Q./.G.S., xlvii, 1891, p. 266 (Shap).
W. J. Sollas : Trans. Roy. Irish Acad., xxix, 1891, p. 427
J. J. H. Teall : Mem. Geol. Surv. (Silurian Rocks, Scotland),
1899, p. 607.
P. J. Holmquist : Bull. Geol. Inst. U-psala, vii, 1906, p. 77
Mem. Geol. Surv., 351, 352 (Land's End), 1907, p. 40.
Mem. Geol. Surv., 347 (Bodmin and St. Austell), 1909, p. 54.
R. H. Rastall : Q.J.G.S., Ixvi, 1910, p. 116 (Skiddaw).
Mem. Geol. Surv., 338 (Dartmoor), 1912, pp. 27 and 37.
Mem. Geol. Surv. Scot., 53 (Glen (Joe), 1916, pp. 119 and 135.
P. Geijer : Bull. Geol. Inst. U$sala, xv, 1916, p. 47 (Sweden,
Mechanics of Intrusion).
R. H. Rastall & W. H. Wilcockson : Q.J.G.S., Ixxi, 1917,
p. 592 (Lake District).
Granite-porphyry. A rock differing from quartz-
porphyry by its relative abundance of phenocrysts
of granitic minerals, and by a generally coarser
groundmass ; = porphyritic micro granite , which
no THE NOMENCLATURE OF PETROLOGY
passes into porphyritic granite as the groundmass
Granitic = Granitoid. - - Terms applied to irregularly
granular textures like that of a non-porphyritic
granite -y Eu granitic = Allotrionwrphic- granular.
Granltite. Originally used to connote granitic rocks
rich in oligoclase, the term is now applied to
biotite-granite as denned by Rosenbusch.
Granodiorite, Becker. A rock intermediate in com-
position between quartz-diorite and quartz-mon-
zonite, and in which the ratio of orthoclase to
plagioclase falls between a third and a seventh.
The term, however, is rarely used in this strict
sense, and is more usually applied to rocks inter-
mediate between quartz-diorite and granite.
Granodolerite, Shand, 1917. A term suggested for
oversaturated dolerites containing quartz and
orthoclase, these minerals being generally pre-
sent, but not necessarily, as interstitial micro-
Granogabbro, ]okannsen, 1917. -- A term suggested
for quartz-orthoclase-gabbros, i.e., for phanero-
crystalline igneous rocks intermediate between
quartz-labradorite-monzonite and quartz-gabbro.
Granoiite, Pirsson, 1899. A general term suggested
for phanerocrystalline igneous rocks having a
granitic as opposed to a porphyritic texture ;
Plutonic rock (in part).
L. V. Pirsson : Journ. Geol., vii, 1899, p. 141.
W. H. Turner : Journ. GeoL, viii, 1900, p. 105.
Granophyre, Rosenbusch, 1872. - - A fine-grained
granitic rock having a micrographic texture, or a
granite- or quartz-porphyry having a micro-
graphic groundmass. In an earlier usage of the
term (Vogelsang, 1867) it connoted a porphyritic
rock having a granitic composition, with a micro-
granular groundmass. Cf. Graphophyre. Grano-
phyres are frequently associated with gabbros and
corresponding 1 to this and to their comparatively
THE NOMENCLATURE OF PETROLOGY in
shallow origin, their chief mafic constituent is fre-
quently augite ; biotite-bearing varieties, however,
are not uncommon.
A. Harker : Q.J.G.S., li, 1895, p. 125 (Carrock Fell).
T. H. Holland : Q.J.G.S., liii, 1897, p. 416.
Mem. Geol. Sur-v. (Tert. Ig. Rocks, Skye), 1904, p. 153.
R. H. Rastall : Q.J.G.S., Ixii, 1906, p. 253 (EnnerdaleV
A. R. Dwerryhouse : Q.J.G.S., Ixv, 1909, p. 55 (Eskdale).
Granophyric. See Micrographic.
Granularity. One of the features involved in the con-
ception of texture ; the effect due to the magnitudes
of the constituent crystals ; described by terms
such as phanerocrystalline, microcrystaUine, etc.
A. L. Queneau : School of Mines Quarterly, xxiii, 1902, p.
Granular Texture. A texture due to the aggregation
of mineral grains of approximately equal size,
whether in clastic, igneous, or recrystallised rocks.
W. Cross : U.S.G.S., iqth Ann. Re<p. (1892-3), p. 232.
Granulation. The fragmentation of minerals strained
beyond their elastic limit. The amount of granula-
tion depends not only on the nature of the stresses,
but also on the minerals themselves and their sizes
C. R. Van Hise : U.S.G.S. Mon., xlvii (Metamorphism),
1904, pp. 673 and 737.
Granulite, Weiss. A granulose metamorphic rock
composed of even-sized interlocking granular
minerals (e.g. , felspars, pyroxenes, and garnet).
Parallel or banded structure is due either to the pre-
sence of streaks and lenticles of non-granular
quartz, or to the alternation of bands in which dif-
ferent minerals predominate ; =Leptynite. The
term granulite has been applied to muscovite-
granites by Michel-LeVy.
Mem. Geol. Surv. (N.W. Highlands), 1907, p. 64.
Granulitic Structure. A structure due to the produc-
tion of granular fragments in a rock by crushing.
In France the same term has also been used as
synonymous with panidionwrphic- granitic texture.
ii2 THE NOMENCLATURE OF PETROLOGY
Granulitic Texture, Judd, 1886. A doleritic or
basaltic texture due to the arrangement of granular
crystals of augite or olivine between a network of
felspar laths. Cf. Inter granular.
J. W. Judd: Q.J.G.S., xlii, 1886, p. 68.
Granulose Structure. A structure characteristically
developed in granulites, due to the presence of
granular minerals, such as quartz, felspars, gar-
nets and pyroxenes, in alternating streaks and
bands developed on a megascopic or microscopic
scale. Successive layers may differ in colour, tex-
ture, or mineral composition, but typical foliation
is absent on account of the absence of lamellar or
Graphic Granite. A phanerocrystalline quartz-alkali-
felspar rock, in which large crystals of the two
minerals are intergrown in such a way that in sec-
tion the intercalates of quartz have the appearance
of cuneiform or Semitic characters.
E. S. Bastin : Journ. Geol., xviii, 1910, p. 313.
A. Holmes : Q.J.G.S., Ixxiv, 1918, p. 77.
Graphic Texture. The cuneiform appearance seen in
section, due to the interpenetration of quartz and
felspar on a megascopic scale. Similar textures,
though generally less regular, are sometimes
developed between certain other pairs of minerals,
the conditions necessary for the development of
graphic and allied textures including the simul-
taneous crystallisation of the minerals concerned
from their eutectic. It does not follow, however,
that graphic texture is a necessary consequence of
Graphophyre, C.I.P.W., 1903. A term suggested in
place of granophyre (Rosenbusch). The latter
term was used by Vogelsang for porphyritic micro-
granitic rocks, but as this usage has not been
generally adopted, and the term granophyre is now
universally used in its Rosenbusch sense, no con-
fusion is caused by its retention. The terms
THE NOMENCLATURE OF PETROLOGY 113
graphophyre and graph ophyric have not yet been
justified by usage, even though their derivation is
more accurately descriptive.
Gravel.- A loose detrital sediment in which the pre-
dominant grade-size is from 2 to 10 mm. A
deposit of more coarsely graded detritus is
described as a pebble-bed, or a boulder-bed. Both
stratigraphically and commercially, however, the
term gravel is used to cover a wider range of
grade-sizes than that defined above.
Graywacke. A term applied to felspathic or tufface-
ous grits and coarse sandstones, usually dark in
colour, which are strongly cemented, often with an
argillaceous binding, and occur characteristically
among the older formations = Grau i wacke.
Greenalite Rock. A dull dark-green rock of uniform
fine grain and conchoidal fracture, containing
grains of greenalite in a matrix of chert, car-
bonate-minerals, and ferruginous amphiboles.
C. R. Van Hise & C. K. Leith : U.S.G.S., Mon. Hi, 1911,
pp. 165, 474.
Green Mud. A deep sea terrigenous deposit, char-
acterised by a considerable proportion of glau-
conite ; CaCO 3 present in variable amounts up to
50 per cent.
J. Murray & A. F. Renard : " Challenger " Re-p. (Deep Sea
Deposits), 1891, p. 236.
Greensand. A general term for sandstones which,
when un weathered, have a greenish hue due to the
presence of kernels and grains of glauconite.
Green Schist. A general term for those varieties of
schists in which hornblende, chlorite, or epidote are
Greenstone. An old field-term applied to more or less
altered basaltic or doleritic rocks, the characteris-
tic dark green colour being due to the presence of
chlorite, hornblende, epidote, etc., as in diabase
G. H. Williams : U.S.G.S. Bull., 62, 1890.
J. S. Flett : Mem. Geol. Surv. (Land's End), 1907, p. 31.
ii4 THE NOMENCLATURE OF PETROLOGY
Werner. - - A primary or pneumatolytirally-
altered rock of granitic or aplitic texture, contain-
ing- quartz, and alkali-micas, and generally, though
not necessarily, topaz. The process whereby
igneous emanations transform granite into greisen
is called greisening or greisenisation.
J. S. Flett : Mem. Geol. Surv. (Bodmin & St. Austell), TQOO,
Griquaite, Beck, 1907. A phanerocrystalline gar-
net-diopside rock (with or without olivine or
phlogopite) occurring as nodular xenoliths in
kimberlite pipes and dvkes. A variety of Ariegite.
T. G. Bonney : Proc. Roy. Soc., A., Ixv, iqoo, p. 223.
P. A. Wagner : The Diamond Fields of S. Africa, 1014, p.
Grit. - - This term has been used with many different
connotations : for coarse-grained sandstone ; for
sands and sandstones, coarse or fine, made up of
angular grains ; for sandstones with calcareous
cement ; and for sandstones with grains of con-
spicuously unequal sizes. Stratigraphically it
appears in the names of formations so different and
variable in grade, angularity, and composition as
Millstone Grit, Coniston Grit, Skiddaw Grit, Pea
Grit, and Trigonia Grit. By Lyell the term was
adopted for coarse-grained sandstones, and there
is now a tendency to restrict it for petrographic
purposes to the cemented detrital sediments cor-
responding- in grade to very coarse sand. Manv
authors, however, prefer to use the term for loose
or cemented sediments which are " gritty " on
account of the angularity of the grains.
Grorudite, Brogger, 1894. - - A microgranitic dyke-
rock, containing- prisms of aeg-irine, and, when
porphyritic, having phenocrysts of alkali-felspar
and aegirine. (Grorud, Christian ?a.)
W. C. Brogger : Eruftivgest . Krisfiania, i, 1894, p. 6.
THE NOMENCLATURE OF PETROLOGY 115
Ground-water. A general term for the water occupy-
ing the interstices and other openings of rocks
below the water table ;- Phreatic water.
For a general classification and discussion of ground-waters,
see R. A. Daly : Econ. Geol., xii, 1917, p. 487.
Guano. A phosphatic deposit, formed from the drop-
pings of sea-fowl in arid regions, which may be
friable or compact according to its age and the
degree of alteration it has suffered by weathering.
Habit. -- A term connoting the sum of the external
characteristics of a mineral or rock. In its appli-
cation to rocks the term implies more than struc-
ture or texture, including also other features which
control the outward appearance, such as lustre,
degree of alteration, and fracture. Habit may be
described broadly by general terms, such as
cenotypal and paleotypal ; or particularly by terms
referring to the appearance of well-known types,
e.g. t tinguaitic habit, aplitic habit, pegmatoid
Halleflinta. -- A term applied to granulose rocks of
horny aspect which are compact or porphyritic, and
sometimes banded. The mineral composition,
quartz, felspar, micas, chlorite, etc., indicates a
metamorphic origin from quartz-porphyry, rhyolite,
or corresponding volcanic tuffs.
Halleflintgneiss. A term formerly used in Sweden
for rocks that are not called leptites.
Haloes. See Pleochroic Haloes.
Haplite. See Aplite.
Harrisite, Harker, 1908. A phanerocrystalline rock
composed essentially of black lustrous cleavable
olivine with anorthite and a little augite ; =
anorthite peridotite. (Harris, Rum.)
A. Harker : Mem. Geol. Surv. Scot., 60 (Small Isles), 1908,
u6 THE NOMENCLATURE OF PETROLOGY
Hartschiefer. A strongly banded and partly schistose
rock due to dynamic metamorphism, and asso-
ciated with other rocks of mylonitic habit, in which
the alternating- bands have been produced from
ultramylonite by recrystallisation and metamorphic
P. Quensel : Bull. Geol. Inst. U-psala, xv, 1916, p. 104.
Harzburgite, Rosenbusch, 1887. -- A peridotite con-
sisting- of olivine and orthorhombic-pyroxene ; =
Hatherlite, Henderson, 1898. A term originally sug-
gested for rocks now known as leeuwfonteinite ;
Hauynophyre, Rammelsberg. An analogue of neph-
elinite, in which the place of nepheline is largely
taken by haiiyne and nosean.
Hawaiite, Iddings, 1913. -- A general term for rocks
of basaltic texture (as contrasted with typical an-
desite texture), in which the felspar is andesine.
Heavy Liquids. A group of heavy organic liquids,
inorganic solutions, and fused salts (heavy melts]
used for the determination of the specific gravity
of mineral particles, or for the separation of
minerals, having respectively lower and higher
specific gravities than the liquid used, e.g.. Bromo-
form, Thoulet Solution, Klein Solution, Mercurous
Hedrumite, Brogger, 1890. A leucocratic variety of
alkali-syenite containing accessory nepheline.
(Hedrum, S. Norway.)
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 183.
Helicitic Structure. A structure of metamorphic
rocks due to the presence in porphyroblastic con-
tact minerals of strings of inclusions representing
an earlier schistosity of the rocks.
A. Backstrom : Geol. Foren i Stockholm ForhandL, xl, 1918,
THE NOMENCLATURE OF PETROLOGY 117
Hemicrystalline. A term applied to igneous rocks to
denote that they consist partly of crystals and
partly of glass or devitrified glass.
Heptorite, BUSZ, 1904. A melanocratic hauyne-basa-
nite containing phenocrysts of barkevikite, titan-
augite and hauyne, in a glassy or analcitic ground-
mass containing microlites of labradorite.
(Rhonderfer Thai, Siebengebirge.)
K. Busz : Neues Jahr., ii, 1904, p. 91.
Heronite, Coleman, 1899. A dyke rock consisting of
spheroidal groups of orthoclase in a base of anal-
cite containing radiating bundles of labradorite
and, in smaller quantity, aegirine ; since shown to
be an altered tinguaite.
(Heron Bay, Ontario.)
A. P. Coleman : Journ. GeoL, vii, 1899, p. 431;.
E. A. Barlow : Cong. Geol. Inter., xii, Guide 8, 1913, p. 17.
Heteromorphic, Lacroix, 1917. -- A term applied to
rocks of similar chemical composition, but of dif-
ferent mineral composition ; as, for example, where
leucite and olivine in one rock may be represented
by biotite in another.
A. Lacroix : C.R., clxv, 1917, p. 486; clxx, 1920, p. 23.
Heumite, Brogger, 1898. A fine grained melanocra-
tic dyke-rock composed of alkali-felspars, nephe-
line, and sodalite, with barkevikite, biotite, and
augite as abundant mafic constituents.
(Heum, S. Norway.)
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 90.
Hexahedrite, Rose. - - A group name for those iron
meteorites which have a cubic cleavage, and which,
on being etched, reveal a system of fine lines
(Naumann Lines) due to twinning parallel to the
Hiatal Fabric, C./.P. IF., 1906. A variety of inequi-
granular texture in which the sizes of the crystals
are not continuously graded, but form a broken
series, as in most rocks exhibiting porphyritic and
J. P. Iddings : Igneous Rocks, I, 1909, p. 198.
ITS THE NOMENCLATURE OF PETROLOGY
Hillhouse Basalt. Hatch, 1892. A type of the Scot-
tish' Carboniferous basalts ; characterised by
numerous micro phenocrysts of olivine and fewer of
aug-ite, in a fine groundmass in which augite pre-
dominates ; = Picrite-basalt .
J. S. Flett : Men?. Geol. Surv. Scot. (Edinburgh), IQIO,
Hirnantite, Cope, 1915. A variety of albite-kerato
phyre, or albitised tholeiite, containing- laths of
sodic plagioclase embedded in an interstitial base
of chlorite, with smaller amounts of calcite, quartz,
leucoxene and haematite.
(Craig-ddu Hirnant, Berwyn Hills.)
T. H. Cope : Proc. Liverpool Geol. Soc. (Cope Memorial
Vol.), 1915, p. 79.
Hogbomitite, Gavelin, 1917. - - See Magnetite-
Holocrystalline. - - A term applied to igneous rocks
completely made up of crystals.
Hololeucocratic, Holomelanocratic, Lacroix, 1902.
Terms applied to facies of igneous rocks, or to
members of a series of related rocks, which are
almost completely composed of lignt or dark
A. Lacroix : Now, Arch, du Mus. d'Hist. Nat., i, TQ02,
Holyokeite, Emerson, 1902. A variety of albite-da-
base containing 70 per cent, albite, 9 per cent,
orthoclase, and 16 per cent, calcite, with smaller
amounts of accessory minerals.
(Holyoke, Mass., U.S.A.)
B. K. Emerson : Journ. Geol., x, 1902, p. t;io.
Homoeoblastic, Becke, 1903. A term used instead of
equigranular and applied to metamorphic rocks to
indicate that the texture so described is due to
recry stall i sat ion.
Hornblende-Schist. A schist in which hornblende is
the dominant mineral : plagioclase and sometimes
quartz being- the chief felsic constituents. With
THE NOMENCLATURE OF PETROLOGY 119
loss of schistose structure the rock passes into
hornblende-gneiss and amphibolite.
J. J. H. Teall : Q.J.G.S., xli, 1885, p. 133.
i'. G. Eonney : Q./.G.S., lii, 1896, p. 18.
J. S. Flett : Mem. Geol. Surv. (Lizard), 1912, p. 44.
Hornblendite, Dana, 1880. A phanerocrystalline ig-
neous rock essentially composed of hornblende.
Olivine-hornblendite is the passage rock to horn-
Hornfels. A contact metamorphosed rock, usually of
speckled granular appearance, but not typically-
schistose, nor strictly granulose, consisting essen-
tially of quartz, micas, and felspars, with or with-
out garnet, andalusite, or cordierite, and more
rarely pyroxene or amphibole. Any cleavage or
incipient schistosity possessed by the parent rock
is obliterated by a new structure which may be
described as maculose.
J. S. Flett : Mem. Geol. Surv. (Dartmoor), 1912, p. 45.
H. Backhand : Geol. Foren i Stockholm Forhandl., xl, 1918,
Hornstone. A general term for compact, tough, sili-
ceous rocks having a splintery or sub-conchoidal
fracture ; distinguished from flint and chert by
greater opacity in thin flakes and the presence of
a veined, banded, or other parallel structure such
as lamination or cleavage.
Howardite, Rose, 1863. - - An achondritic meteorite
containing bronzite, olivine, and anorthite, with
little or no iron.
Hudsonite, Cohen. - The term originally suggested
for rocks now known as Cortlandtite. The latter
term is generally adopted as hudsonite had pre-
viously been given to a variety of pyroxene.
(Hudson R., New York.)
Hullite. A soft dark substance occurring as inter-
stitial matter and amygdaloidal infillings in Antrim
basalts. It is of the same nature as palagonite,
120 THE NOMENCLATURE OF PETROLOGY
but differs from the latter in having a low specific
gravity, viz., 1.76.
(Carnmoney Hill, near Belfast.)
G. A. J. Cole : Rep. Belfast Nat. Field Club, 1894-5, p. i.
J. J. H. Teall : Q.J.G.S., liii, 1897, pp. 485-6.
Humic Coals, Potonie, 1904. -- A group of coals, in-
cluding the ordinary bituminous varieties, which
have been formed from accumulations of vegetable-
debris that have maintained their morphological
organisation with little decay.
Marie C. Slopes & R. V. Wheeler : The Constitution of Coal,
1918, p. 19.
Hunne Diabase, Tornebohm, 1877. A type of quartz-
dolerite containing hornblende, biotite and a little
quartz, in addition to plagioclase and a pale augite
(sahlite). Interstitial chloritic matter is oiten
present, and the type is frequently somewhat
porphyritic in aspect. Cf. Konga Diabase.
Hyalo-. A prefix added to certain rock names to sig-
nify a glassy rock of corresponding chemical com-
position, e.g., hyalo-basalt.
Hyalomelane, Haussmann, 1847. A name given to
basaltic glass at a time when the latter was con-
sidered to be a definite mineral species.
Hyalo-ophitk Texture, Polenov, 1899. A texture re-
sembling ophitic texture, in which the spaces of an
open network of felspar laths are occupied by
glass ; a limiting case of intersertal texture.
Hyalopilitic. A groundmass texture in which laths
or microlites of felspar are interwoven (as in a felt)
with glass occupying the interstices between
Hybrid, Durocher, 1857. A term originally applied to
" intermediate " rocks at a time when they were
regarded as the products of composite magmas
derived from the admixture of the " trachytic " and
" pyroxenic " magmas of Bunsen. By Harker,
1904, the term is adopted for abnormal igneous
THE NOMENCLATURE OF PETROLOGY 121
rocks, of which Marscoite is an example, formed
by the mixture of two magmas, or by the assimila-
tion of a rock already consolidated by the magma
of a later intrusion.
A. Marker : Mem, Geol. Surv. (Tert. Ig. Rocks, Skye), 1904,
Nat. Hist. Ig. Rocks, 1909, p. 333.
Hydatogenesis. The process whereby mineral depo-
sits are formed from magmatic solutions rich in
water. The term is also employed by some au-
thors for all deposits formed from aqueous solu-
tion whether the waters be magmatic, vadose, or
HydatogenoilS, Renevier, 1880. -- A term applied to
chemical deposits of aqueous origin, including
Hydrpthermal. A term applied to magmatic emana-
tions rich in water; to the processes in which they
are concerned ; and to the rocks or ore-deposits,
alteration products, and springs produced by them.
G. W. Morey & P. Niggli : Journ. Am. Chem. Soc., xxxv,
1913, p. 1086.
E. A. Stephenson : Journ. Geol., xxiv, 1916, p. 180.
Hypabyssal. A general term applied to minor intru-
sions, such as sills and dykes, and to the rocks of
which they are made, to distinguish them from
volcanic rocks and formations on the one hand,
and " plutonic " rocks and major intrusions such
as batholiths on the other.
Hyperite, Elie de Beaumont. A term at first synony-
mous with Norite, now extended to include some-
what granular hypersthene-felspar rocks with or
without augite, diallage, or garnet.
J. J. H. Teall : Mem. Geol. Surv. (Sil. Rocks, Scotland), 1,
1899, P- 6l 3-
Hypersthenite. A rock composed wholly or almost
wholly of hypersthene. Small amounts of other
pyroxenes, plagioclase, or olivine may be present.
122 THE NOMENCLATURE OF PETROLOGY
Hypidiomorphic, Rosenbusch. -- A general term ap-
plied to those forms of igneous rock-minerals
which are bounded only in part by their character-
istic crystal faces, i.e., for forms intermediate be-
tween idiomorphic and cdlotriomorphic ; = Sub-
hedral; = Hypautomorphic.
Hypidiomorphic Texture. A texture of igneous rocks
due to the development of the greater proportion of
the minerals in crystals having hypidiomorphic
Hypocrystalline. -- A term applied to igneous rocks
made up partly of crystals and partly of glass.
Hypogene, Lyell, 1833. A general term intended to
include both plutonic and metamorphic classes of
rocks, that is, for rocks formed within the earth.
By A. Geikie, 1879, tne term was use d for geolo-
gical processes originating within the earth, and
if it were applied to rocks in this sense, it would
therefore include volcanic rocks, which were inten-
tionally excluded by Lyell from his hyogene rocks.
Cf. Epigene; Endo genetic.
Hysterobase, Lassen, 1888. A variety of diabase con-
taining plagioclase, quartz, biotite, and brown
hornblende, the latter paramorphic after augite.
Idioblast, Becke, 1903. -- A term applied to pseudo-
idiomorphic crystals, such as garnet, occurring in
metamorphic rocks. An idioblast may be high in
the crystalloblastic order of the minerals present,
but it has no significance in relation to order of
crystallisation, as would be the case in igneous
Idiomorphic, Rosenbusch. A general term applied to
the forms of igneous rock-minerals which are com-
pletely bounded by the crystal faces peculiar to the
species ; = Euhedral ; = Automorphic.
THE NOMENCLATURE OF PETROLOGY 123
Ijolite, Ramsay, 1891. -- A phanerocrystalline rock
essentially composed of nepheline and aegirine-
augite or other pyroxene free or nearly free from
normative plagioclase. Cf. Fasinite.
V. Hackman : Bull. Comm. geol. Finlande, No. n, 1900.
Ijussite, Rakovski, 1911. -- A variety of teschenite-
pyro'xenite containing abundant titanaugite and
barkevikite, with small amounts of bytownite,
anorthoclase and analcite. (Ijuss R., Siberia.)
J. Rakovski : Trans, Mus. Pet. Or. Ac. Sci. St. Pet., v,
1911, p. 256.
Ilmenite-norite, Kolderup, 1896. A variety of norite
(hypersthene and labradorite) with a high percen-
tage of ilmenite varying in different parts of the
rock-mass from 20 to 80 per cent.
Ilmenitite, Kolderup, 1896. A facies of ilmenite-
norite consisting predominantly of ilmenite.
C. F. Kolderup : Bergen Mus. Aarb., v, 1896, p. 178.
Imandrite, Ramsay, 1894. A rock composed of
quartz and albite, due to interaction between a
nepheline-syenite magma and graywacke.
W. Ramsay & V. Hackman : Fennia, xi, 1894, p. 74.
Impregnation. A term expressing the irregular dis-
tribution of introduced mineral matter through a
previously formed rock; contrasted with dissemi-
nation which expresses distribution without
implication as to order of deposition.
Impsonite, Eldridge, 1901. A variety of asphaltite
having a specific gravity of 1.175, characterised by
a hackly fracture, and by being soluble in carbon
disulphide to the extent of about 35 per cent.
G. H. Eldridge : U.S.G.S., 22nd Ann. Re-p., Ft. i, 1901,
Inclusion. A general term for foreign bodies (gas,
liquid, glass, or mineral) enclosed by minerals ;
also extended in its English usage to connote en-
I2 4 THE NOMENCLATURE OF PETROLOGY
closures of rocks and minerals within igneous
rocks, such as cognate and accidental inclusions.
It is, however, desirable to distinguish inclusions,
enclosures, and segregations (q-v.).
J. A. Smythe : Geol. Mag., 1914, p. 244.
S. Powers : Journ. Geol., xxiii, 1915, p. i.
Indurated. A term technically restricted to compact
rocks that have been hardened by the action of
Ingenite, Forbes, 1867. A general term for igneous
rocks "born, bred, or created within or below."
By Kinahan, 1873, the term was extended to in-
clude metamorphic rocks as well as the igneous
rocks alone considered by Forbes. Cf. Derivate.
Injection Gneiss. A gneiss whose banding is wholly
or partly due to the lit-par-lit, or interlaminar, in-
jection of granitic magma into schistose, fissile,
or otherwise penetrable rocks ; = (in part) Com-
Inninmorite, Thomas & Bailey, 1915. A porphyri-
tic rock containing phenocrysts of plagioclase
(labradorite to anorthite) and augite, in a ground-
mass of more sodic plagioclase, augite, and abun-
dant glass. (Inninmore, Morven.)
E. M. Anderson. & E. G. Radley : Q.J.G.S., Ixxi, 1916, p. 205.
Intercalate. A term applied generally to a body of
one kind of material interlaminated with another ;
and particularly to lamellar inclusions of one mine-
ral in another, the former being orientated more or
less exactly in planes related to the crystal struc-
ture of the latter, e.g., in perthite (intercalates of
plagioclase in orthoclase), and in certain minerals
characterised by schiller structure.
Intergranular, Evans, 1916. A texture characteristic
of holocrystalline basalts and doleritic rocks, due
to the aggregation of grains of augite (not in opti-
cal continuity, as in sub-ophitic texture) between
felspar laths arranged in a network that may be
diverse, sub-radial, or sub-parallel; distinguished
THE NOMENCLATURE OF PETROLOGY 125
from inters e rial by the absence of interstitial glass,
or other substances that take the form of the inter-
stitial spaces. Cf. Granulitic Texture.
A. Holmes : Min. Mag., xviii, 1918, p. 191.
Intersertal, Zirkel, 1870. A texture characterised by
the insertion between divergent laths of felspar of
glass, palagonite, chlorite, or other primary or
secondary minerals that take the form of the inter-
stitial spaces. In intersertal basalts, the grains
of augite rarely occupy the wedge-shaped spaces
completely, continuity being established by a
mesostasis of glass or its alteration products.
Intratelluric, Rosenbusch. A term applied to the
period of crystallisation of a magma anterior to its
effusion as a lava, and represented in many vol-
canic rocks by phenocrysts formed under com-
paratively deep-seated conditions. Such crystals,
belonging to an earlier generation than the
groundmass, are also described as intratelluric.
Isenite, Bertels, 1874. A felspathoid-bearmg variety
of hornblende-trachyandesite, having phenocrysts
of andesine, soda-microline, hornblende and
biotite, in a groundmass of oligoclase, orthoclase,
and nosean, with small amounts of augite, apatite
and iron-ores. (Nassau.)
IsomorphoilS. A term applied to two or more
minerals or other crystalline bodies which form an
isomorphous series when they are related by close
similarity of chemical constitution, and crystallise
in the same class of the same system of symmetry,
developing the same forms with angles that differ
by not more than, a few degrees. Such minerals
can form intimate crystalline mixtures or solid
solutions (e.g. , albite and anorthite), in which the
physical properties change continuously with the
composition. Certain minerals are imperfectly
isomorphous (e.g., atbite and orthoclase) when one
126 THE NOMENCLATURE OF PETROLOGY
or more of the above criteria fails to hold, and
only a limited amount of one mineral is capable of
being molecularly dispersed through the other.
A. L. Day & E. T. Allen : Am. Journ. Sci., xix, 1905, p. 93
A. L. Day : Bull. GeoL Soc. Am., xxi, 1910, p. 147.
A. E. II. Tutton : Crystalline Structure and Chemical Con-
stitution, 1910, p. 124.
Issite, Duparc & Pamfil, 1910. A melanocratic
dyke rock containing hornblende, with a smaller
quantity of green pyroxene and a variable but al-
ways subsidiary amount of labradorite ', = melano-
cratic hornblende- gabbro, or felspathic hornblen-
L. Duparc & P. Pamfil : C.R., cli, 1910, p. 1136; Bull. Soc.
Min. France, xxxiii, 1910, p. 351.
Itabirite, Eschivege. A variety of quartzite contain-
ing abundant iron-ore minerals, with accessory
oligoclase and muscovite. (Itabira, Brazil.)
Itacolumite, Humboldt. - - A schistose and flexible
variety of quartzite containing micaceous minerals
(mica, chlorite, talc) in addition to the chief con-
stituent, quartz. (Mt. Itacolumi, Brazil.)
R. D. Oldham : Rec. GeoL Surv. India, xxii, 1889, p. 51.
G. W. Card : GeoL Mag., 1892, p. 120.
Invernite, Watts, 1895. A holocrystalline intrusive
rock of granitic aspect containing phenocrysts of
orthoclase and fewer of plagioclase in a ground-
mass consisting of stumpy idiomorphic felspars
(mostly orthoclase but in part plagioclase),
sparsely distributed hornblende or mica, and in-
W. W. Watts : In Guide to the Collections of Rocks and
Fossils, Gecl. Surv. Ireland, 1895, p. 93.
JaCUpirangite, Derby, 1891. -- A term applied to a
melanocratic series of igneous rocks of varying
composition, the characteristic minerals being
purple titanaugite, nepheline, and magnetite or
THE NOMENCLATURE OF PETROLOGY 127
titanoferrite. The chief types range from ijolite-
like rocks (pyroxene-nepheline rocks with some
biotite and olivine) to alkali-pyroxenites, and from
each of these to varieties rich in magnetite.
H. S. Washington : Journ. Geol., ix, 1901, p. 620.
Jadeitite. A rock consisting of the alkali-pyroxene
jadeite associated with small amounts of felspar or
felspathoid, and probably derived from alkali-
igneous rocks by high-pressure metamorphism.
Jasperisation. The alteration of rocks, igneous or
sedimentary, into banded jaspilite-like rocks by
metasomatic processes in which iron-oxides and
silica are successively introduced.
A. E. V. Zealley : Trans. Geol. Soc. S. Africa, xvi, 1918,
Jasperoid. A term sometimes used for limestones and
calcareous rocks., in which the carbonates have
been replaced by fine-grained quartz aggregates or
chalcedony. Rocks of this kind are generally
grey, and chert-like in appearance, and they are
often developed as the gangue of metasomatic
sulphide deposits, particularly those of the silver-
Jaspilite. A term applied to rocks composed of inter-
banded layers respectively rich in silica (quartz or
chalcedony) and iron-oxides (magnetite, haematite,
etc.). The chert-like bands have a red colour
owing to the inclusion of flakes of haematite.
Variable amounts of ferruginous amphiboles are
generally present, and the rocks are not only
conspicuously banded, but are often contorted and
C. R. Van Hise & C. K. Leith : U.S.G.S., Mon. Hi, 1911,
PP- 124, 464, 466.
C. R.- Van Hise : Journ* and Proc. Roy. Soc. West Aust.>
ii, p. 23.
128 THE NOMENCLATURE OF PETROLOGY
Jedburgh Basalt, Watts, 1897. A type of the Scot-
tish Carboniferous basalts ; characterised by in-
conspicuous phenocrysts of olivine and plagioclase
in an ophitic to microlitic groundmass, to which
augite is almost always restricted.
E. B. Bailey : Mem. Geol. Surv. Scot. (Glasgow District),
1911, p. 138.
G. W. Tyrrell : Trans. Geol. Soc. Glasgow, xiv, 1912, p. 226.
Jet. A hard coal-black variety of lignite, showing the
structure of coniferous wood under the microscope.
Mem. Geol. Surv. S-pec. Re-p., Mineral Resources of Great
Britain, vii, 1918.
Josefite, Szadeczhy, 1899. An altered microgranular
dyke rock consisting of augite and olivine, with
abundant serpentine and calcite. (Assuan.)
Jtimillite, Osann, 1906. A fine-grained porphyritic
rock containing phenocrysts of orthoclase (with
poikilitic inclusions of olivine), phlogopite and
soda-pyroxenes and amphiboles in a matrix of
soda-amphibole and leucite, with accessory apatite
and titanoferrite. (Jumilla, Murcia, Spain.)
A. Osann : Festschrift H. Rosenbusch, 1906, p. 263.
Juvenile, Suess, 1902. A term applied to water and
other volatile materials that are known to be mag-
matic emanations of primary endogenetic origin.
Those of secondary endogenetic origin occurring
as emanations derived from country rock are dis-
tinguished by Daly as Resurgent.
R. A. Daly : Econ. Geol., xii. 1917, p. 489.
Kaiwekite, Marshall, 1906. An olivine-bearing variety
of alkali-trachyte or trachyandesite, approximately
representing the volcanic equivalent of laurvikite.
The rock contains phenocrysts of anorthoclase,
titanaugite mantled with segirine, barkevikite, and
olivine, in a groundmass of oligoclase with small
amounts of pyroxene and magnetite.
(North Head, Otago, N.Z.)
P. Marshall : Q.J.G.S., Ixx, 1914, p. 390.
THE NOMENCLATURE OF PETROLOGY 129
Kakirite, Svenonius. A megascopically sheared and
brecciated cataclastic rock in which fragments of
the original material are surrounded by innumer-
able gliding surfaces in which intense granulation
and some recrystallisation have taken place.
(Lake Kakir, Swedish Lapland.)
P. Quensel : Bull. Geol. Inst. Upsala, xv, 1916, p. 100.
Kakortokite, Ussing, 1911. A banded nepheline-
syenite containing leucocratic layers rich in felspar
and nepheline (white), others rich in eudialite and
nepheline (red), and melanocratic layers rich in
aegirine and arfvedsonite (black).
N. V. Ussing : Medd. om Gronland, xxxviii, 1912, p. 177.
Kankar. A vernacular Indian term for stone; now
restricted to concretionary masses of calcium car-
bonate occurring in alluvium ; = Kunkar.
Kaolin. Kaolin is a white, or slightly stained, clay,
due to the decomposition of a highly felspathic
rock, and therefore also* containing a variable pro-
portion of other constituents! derived from the
parent rock. The clay-substance itself is
essentially a hydrated silicate of alumina, and to
this material the name kaolinite is frequently
given. The word kaolin is derived from the
Chinese kuling, meaning " high ridge," the ridge
referred to, near Jaochau Fu, having been wrongly
considered to be the site of an, important deposit
which actually lies at the foot of the ridge. See
J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and
China Stone), 1914.
W. R. Jones : Clays of Economic Im-portance in the F .M.S.,
Govt. Press, Kuala Lumpur, 1915.
Kaolinisation. The processes whereby felspars, and
other alumino-silicates, are altered to kaolin.
J. A. Howe : Mem. Geol. Surv. (Kaolin, China Clay and
China Stone), 1914, p. 135.
Karite, Karpinsky, 1904. A variety of grorudite con-
taining about 50 per cent, of quartz.
(R. Kara, Siberia.)
i 3 o THE NOMENCLATURE OF PETROLOGY
Kassaite, Lacroix, 1918. A microlitic dyke-rock con-
taining- phenocrysts of hauyne, barkevikite, augite
and labradorite in a groundmass of hornblende and
felsic minerals. (Los Archipelago.)
A. Lacroix : C.R., clxvi, 1918, p. 542.
Kata-, Grubenmann, 1907. A prefix used as a qualifier
to the group-names suggested by Grubenmann for
metamorphic rocks, to indicate that the type so
distinguished belongs to the deepest zone of meta-
morphism. In this, zone the distinctive physical
conditions are very high temperature and hydro-
static pressure, and comparatively feeble stress,
and the rocks characteristically produced include
biotite-, sillimanite-, cordierite-, garnet-, and
pyroxene-gneiss, granulites, and eclogite. Cf.
Epi-j and Meso-.
U. Grubenmann : Die Kristallinen Schiefer, II, 1907, pp.
Kataclastic. See Cataclastic, Kjerulf.
KatagneisS. A term applied to gneisses, amphibolites,
etc., considered to have been formed in the deep-
est zone of metamorphism, where high tempera-
ture is a controlling factor, and high hydrostatic
pressure dominates over shearing stress. (Note
the different sense in which kata- is used in the
Katamorphism, Van Hise, 1904. - - The alteration of
rocks by weathering and cementation, the charac-
teristic changes involving the production of simple
compounds from more complex minerals.
C. R. Van Hise: U.S,G.S. Man., 47, 1904.
C. K. Leith & W. J. Mead : Metamorphic Geology, 1915.
Katzenbuckelite, Osann, 1903. A porphyritic rock of
tinguaitic habit having phenocrysts of nepheline,
nosean, biotite, and olivine, in a glassy or crypto-
crystalline groundmass containing minute crystals
of nepheline, leucite, orthoclase, biotite and soda-
pyroxenes and amphiboles.
(Katzenbuckel, Odenwald, Baden.)
A. Osann : Tschermak's Min. Pet. Mitt., xxi, 1903, p. 365.
THE NOMENCLATURE OF PETROLOGY 131
Kauaiite, Iddings, 1913. A coarse gabbro-like rock
containing- augite and olivine and zoned felspars
ranging from calcic labradorite in the inner to
alkali-felspar in the outer zones ; = olivine-augite-
diorite. (Hawaiian Is.)
W. Cross : U.S.G.S., Prof. Pap., 88, 1915, p. 15.
Kedabeldte, Fedorof, 1901. A garnetiferous variety
of gabbro or eucrite, in which the plagioclase is
anorthite. (Kedabek Caucasus.)
Kelyphitic, Schrauf, 1882. - - A term applied to the
" rims " or " borders," composed of microcrystal-
line aggregates of pyroxene or amphibole, which
sometimes appear around olivine where it would
otherwise be in contact with plagioclase, or around
garnet where it would otherwise be in contact with
olivine or other mag-nesium-rich minerals. Bonney
suggests that the term be restricted to occurrences
of secondary origin, applying the term Corona to
those that are primary.
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916,
Kentallenite, Hill & Kynaston, 1900. A phanero-
crystalline rock consisting essentially of olivine
(dusty in thin section), pale-green augite, biotite,
plagioclase, and orthoclase. Some varieties may
be regarded as melanocratic olivine-monzonite, but
in others orthoclase is inconspicuous or occultl
(Kentallen, Loch Linnhe.)
J. B. Hill & K. Kynaston : Q.J.G.S., Ivi, 1900, p. 531.
Kenyte, Gregory, 1900. A variety of alkali-trachyte,
containing phenocrysts of anorthoclase in a hyalo-
pilitic or trachytic base. ^Egirine-augite is pre-
sent, and, in some varieties, olivine.
(Mt. Kenya, B.E.A.)
J. W. Gregory : Q.J.G.S., Ivi, 1900, p. 205.
G. T. Prior : Min. Mag., xiii, 1902, p. 246.
Keralite, Cordier, 1868. A variety of hornfels having
quartz and biotite as its essential minerals.
Keratophyre, Gumbel, 1874. - - A soda-porphyry or
trachyte containing albite-oligoclase or anortho-
i 3 2 THE NOMENCLATURE OF PETROLOGY
clase in an orthophyric or felsitic groundmass ;
pyroxenes, often altered to chlorite, epidote,
etc., may be present.
A. H. Cox : Re-p. Brit. Assoc. (Birmingham, 1913), 19145 p.
Kersantite, Deles se, 1851. A dioritic lamprophyre
characterised by biotite and plagioclase.
Khagiarite, Washington, 1913. A black vitreous
variety of pantellerite containing phenocrysts of
soda-microcline, diopside, segirine-augite, and
cossyrite, in a groundmass of brown glass having
a flow texture due to the arrangement of micro-
lites or crystallites. = Hyalo-pantellerite.
H. S. Washington : Journ. GeoL, xxi, 1913, p. 708.
Khondalite Series, Walker, 1902. A series of meta-
morphic rocks (named after the Khonds of India,
in whose country they occur), consisting of garnet-
quartz-sillimanite rocks with garnetiferous quartz-
ites, graphite-schists and calciphyres.
T. L. Walker : Mem. Geol. Surv. India, xxxiii, 1902, p. n.
Kidlaw Basalt, Bailey, 1910. A type of the Scottish
Carboniferous analcite-basalts ; characterised by
numerous microphenocrysts of olivine and augite
in a groundmass notable for the relative abund-
ance of orthoclase and biotite and the presence of
analcite in large poikilitic crystals.
E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), 1910,
Kieselguhr. See Diatomite.
Killas. A Cornish mining term for the altered,
schistose, or hornfelsic rocks in contact with
granite, and often considerably modified by emana-
tions from the latter.
Kilsyth Basalt, Watts, 1897. A variety of the Markle
type (q.v.) of the Scottish Carboniferous basalts,
characterised by sub-ophitic texture.
THE NOMENCLATURE OF PETROLOGY 133
Kimberlite, Carvill Lewis, 1887. A brecciated biotite-
peridotite, occurring in the diamond-pipes of South
P. A. Wagner : The Diamond Fields of S. Africa, 1914,
D. Draper & W. H. Goodchild : Mining Journ.. cxiii, 1916,
PP- 357, 3 6 S-
Kinne Diabase, Tornebohm, 1877. A type of olivine-
diabase containing intersertal chloritic matter and
Kinzigite, Fischer, 1860. A coarsely granulose rock
formed by the metamorphism of sedimentary rocks
of appropriate composition, and essentially com-
posed of garnet and biotite, with varying amounts
of quartz, orthoclase, oligoclase, muscovite,
cordierite, or sillimanite. (Kinzig-, Schwarzwald.)
Klein Solution. A yellow aqueous solution of cad-
mium boro-tungstate, somewhat viscous when
saturated, having a maximum specific gravity of
W. B. D. Edwards : Geol. Mag., 1891, p. 273.
Knotted Schist or Knotenschiefer. See Spotted
Kodurite, Fermor, 1907. The type rock of the Ko-
durite Series, composed of potash felspar, spandite
(a garnet intermediate between spessartite and
andradite), and apatite.
(Kodur Mines, Vizagapatam, India.)
L. L. Fermor : Rec. Geol. Surv. India, xlii, 1912, p. 208.
Kodurite Series, Fermor, 1907. A series of rocks of
uncertain but probably igneous origin, associated
with the Archaean complex of Madras, and ranging
from quartz-orthoclase rocks through Kodurite to
spandite-rock and manganese-pyroxenites.
L. L. Fermor : Mem. Geol. Surv. India, xxxvii, 1909, p.
Kohalaite, Iddings, 1913. A general term for oligo-
clase-andesites. (Kohala Mt. , Hawaiian Is.)
Kolm. A variety of coal occurring locally as lenticles
in Swedish alum-shales, and containing about 30
i 3 4 THE NOMENCLATURE OF PETROLOGY
per cent, of ash, which is remarkable for its high
content of rare metals, including- uranium and
Konga Diabase, Tornebohm, 1877. A type of grano-
dolerite containing calcic labradorite laths and in-
tergranular augite (sahlite) and orthorhombic
pyroxene, in a microgranitic interstitial mass of
quartz and orthoclase. Cf. Hunne diabase.
Koswite, Duparc, 1902. -- A variety of olivine-pyro-
xenite containing diopside as its chief constituent
with olivine in moderate amount, and magnetite
acting as an interstitial cement.
(Koswinsky, N. Urals.)
L. Duparc & P. Pamfil : Bull. Soc. Min. France, xxxiii,
1910, p. 251.
Krablite, Forchhammer, 1832. A variety of crystal-
tuff containing abundant sanidine, with plagio-
clase, augite, and quartz in smaller proportions.
(Mt. Krabla, Iceland.)
Krageroite, Brogger, 1904. An albite-aplite in which
the place of quartz is largely taken by rutile ; =
Kragerite. (Kragero, S. Norway.)
T. L. Watson : Am. Jottrn. Sci., xxxiv, 1912, p. 509.
Kulaite, Washington, 1894. A nepheline- or leucite-
bearing trachydolerite in which hornblende is the
dominant mafic mineral ; varieties in which ortho-
clase cannot be recognised resemble tephrite.
(Kula Devit, Lydia, Asia Minor.)
H. S. Washington : Journ. GeoL, viii, 1900, p. 610.
Kullaite, Hennig, 1899. A variety of diabase contain-
ing red phenocrysts of plagioclase and microcline.
Kunkar. See Kankar.
Kuskite, Spurr, 1900. A term applied to quartz- or
adamellite-porphyry containing primary scapolite.
(Kusko R., Alaska.)
J. E. Spurr: Am. Journ. Sci., x, 1900, p. 315; U.S.G.S.,
zoth Ann. Re-p., Pt. vii, 1900, p. 221.
THE NOMENCLATURE OF PETROLOGY 135
Kvellite, Brogger, 1898. A porphyritic syenite-lam-
prophyre containing olivine, barkevikite, lepido-
melane, apatite and magnetite in a groundmass of
anorthoclase laths. Cf. Tjosite.
(Near Lougental, Christiania District.)
Kylite, Tyrrell, 1912. A melanocratic olivine-essexite
with abundant labradorite, titanaugite, and oli-
vine, and small amounts of nepheline and analcite.
Cf. Luscladite. (Kyle district, Ayrshire.)
G. W. Tyrrell : Geol. Mag., 1912, p. 121.
Kyschtymite, Moroziewicz, 1897. A phanerocrystal-
line rock composed of anorthite, biotite, and
corundum, and smaller amounts of green spinel,
zircon and apatite. (Kyschtym, Urals.)
A. E. Barlow : Geol. Surv. Canada, Mem. 57 (Pub. No.
1022), 1915, p. 231.
Laanilite, Hackman, 1905. A coarse-grained peg-
matoid rock of which the essential constituents are
garnet, biotite, quartz and iron ores.
(Laanila, Finnish Lapland.)
Labile, Ostwald, 1897. A term describing the condi-
tion of a supersaturated solution in which the con-
centration at any given temperature is sufficiently
high to ensure rapid separation of the solute, even
in the absence of the solid phase.
Labradite, Turner, 1900. A phanerocrystalline rock
composed almost entirely of labradorite.
Labradorite, Senft, 1857. As a rock name, this term
is applied by French authors to leucocratic basalts
rich in the mineral labradorite (Fr. labrador) ; by
Russian authors it has been used for leucocratic
varieties of gabbro or norite, i.e., for anorthosite.
Laccolith, Gilbert, 1880. A dome-shaped intrusion
with both floor and roof concordant with the
1 36 THE NOMENCLATURE OF PETROLOGY
bedding planes of the invaded formations, the roof
being arched upwards as a result of the intrusion.
W. Cross: U.S.G.S., i^th Ann. Rep. (1892-3), ii, 1894,
Lakarpite, TSrnebohm, 1906. A phanerocrystalline
rock composed of microcline, oligoclase, and
soda-amphibole ; aegirine or rosenbuschite may
also be present. (Korra Karr, Sweden.)
A. E. Tornebohm : Sveriges Geol. Unders., Ser. C, No. 199,
1906, p. 54.
Lamprophyre, G umbel, 1887. - - A general term for
those facies of holocrystalline dyke-rocks which
differ from the normal types containing the same
essential minerals by the marked abundance of
their mafic minerals, and the frequent presence of
alteration products, especially calcite and those
derived from the felspars.; e.g. , Minette and
A. Harker : Geol. Mag., 1892, p. 199.
T. S. Flett : Trans. Roy. Soc. Edin., xxxix, 1900, p. 865.
J. Morrison : Q.J.G.S., Ixxiv, 1918-19, p. 116.
Landscape Marble. A popular descriptive term ap-
plied to an argillaceous limestone of Liassic age,
found near Bristol (Gotham stone), and charac-
terised by the presence of conspicuous arborescent
B. Thompson : Q.J.G.S., 1, 1894, p. 393.
Lapilli. - - Volcanic ejectamenta consisting of frag-
ments of lava of rounded or irregular shape, vary-
ing in size from that of a pea to that of a walnut.
Lassenite, Wadsworth, 1891. A term proposed for
fresh trachyte-glass, altered forms being termed
metabolite. (Lassen Peak, California.)
Latent Heat. Latent heat is the amount of heat ab-
sorbed or emitted by i gram of a substance at con-
stant pressure and constant temperature during a
THE NOMENCLATURE OF PETROLOGY 137
change of state. The various types of change are
distinguished as follows :
Latent heat of evaporation for the change
Latent heat of sublimation for the change
Latent heat of ftision for the change solid-
Latent heat of solution for the change solute-
Latent heat of transition for the change solid-
Laterite, Buchanan, 1807. A residual deposit, often
concretionary, formed as a result of the decomposi-
tion of rocks by weathering and ground-waters,
and consisting essentially of hydrated oxides of
aluminium and iron, which may be crystalline or
L. L. Fermor : Geol. Mag., 1911, p. 454, p. 507, p. 559; 1915,
p. 28, p. 77, p. 123.
J. M. Campbell : Mining Mag., xvii, 1916, pp. 67, 120, 171,
Lateritic Constituents, Fermor, 1911. -- A term ap-
plied to the hydroxides and oxides of iron, alumi-
nium, titanium and manganese ; these, and espe-
cially the first two, being the essential constituents
of late rite.
Lateritite, Fermor, 1911. - - A detrital and recon-
structed form of laterite.
Lateritoid, Fermor, 1911. A lateritic rock formed by
the metasomatic replacement of some other rock
at its outcrop.
Latite, Ransome, 1898. An andesitic rock of mon-
zonitic composition containing orthoclase as an es-
sential constituent in addition to plagioclase ;
= tr achy ande site.
Laugenite, Iddings, 1913. A general term for oligo-
clase-diorites. (Laugendal, Norway.)
Laurdalite, Brogger, 1890. A variety of nepheline-
syenite with rhombic anorthoclase and any of the
138 THE NOMENCLATURE OF PETROLOGY
following minerals : pyroxene, amphibole and
biotite ; olivine-bearing varieties also occur.
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 7.
Laurvikite, Brogger, 1890. A variety of alkali-syen-
ite composed essentially of rhombic anortho-
clase, aegirine-augite and biotite.
W. C. Brogger : Zeit. /. Kryst. u. Min., xvi (i), 1890; p. 28.
Lavialite, Sederholm, 1899. A metamorphic rock
with relict phenocrysts of labradorite, probably
derived from a basaltic rock or tuff. The pheno-
crysts are penetrated by alteration passages con-
taining quartz, microcline, biotite and hornblende,
and are set in a recrystallised amphibolite-like
groundmass of those minerals, among which green
hornblende is the most conspicuous.
(Kirchspiel, Lavia, Finland.)
E. Makinen : Geol. For. i Stockholm Fork., xxxvii, 1915,
Ledntiorite, Shand, 1910. An altered melanite-augite-
nepheline-syenite associated with borolanite, but
free from the pseudo-porphyritic character of the
latter. (Ledmore River, Assynt.)
S. T. Shand : Trans. Edin. Geol. Soc., ix, 1910, p. 384.
Leeuwfonteinite, Molengraaff, 1904. - - A variety of
alkali-syenite containing barkevikite, and charac-
terised by an abundance of anorthoclase. Por-
phyritic varieties also occur.
H. A. Brouwer : Journ. Geol., xxv, 1917, p. 775.
Leidleite, Thomas & Bailey, 1915. A porphyritic
rock containing phenocrysts of plagioclase (labra-
dorite to anorthite) in a subviarolitic groundmass
of felspar, augite, and glass. (Glen Leidle, Mull.)
E. M. Anderson & E. G. Radley : Q.J.G.S., Ixxi, 1915, p.
Lemberg's Reaction. A test for the discrimination of
calcite and dolomite. Lemberg's Solution, log-
wood digested in an aqueous solution of aluminium
THE NOMENCLATURE OF PETROLOGY 139
chloride, is used as a combined stain and reagent.
Calcite (and aragonite) are stained violet after
treatment for about ten minutes, while dolomite
' remains unchanged.
Lenne Porphyry, v. Dechen. A group name for the
keratophyres and associated crystal-tuffs of the
Lenne Valley, Westphalia.
Leopardite, Hunter, 1853. A variety of quartz-
porphyry containing small phenocrysts of quartz
in a microgranitic or microgranophyric ground-
mass of quartz, orthoclase, albite, and mica. The
rock has a characteristically spotted or streaked
appearance due to staining by hydroxides of iron
T. L. Watson : Journ. Geol., xii, 1904, p. 215.
Lepidoblastic, Becke, 1903. A metamorphic texture
due to the development during recrystallisation of
minerals such as micas and chlorite having a flaky
or scaly habit.
Leptite, Hummel, 1870. A term, used especially by
Swedish and Finnish geologists, applied to fine-
grained granular metamorphic rocks composed
mainly of quartz and felspar with subordinate mafic
minerals ; = Granulite, = Halle flint gneiss.
A. G. Hogbom : Bull. Geol. Inst. U-psala, x, 1910, p. 42.
P. Eskola : Bull. Comm. Geol. F inlands, No. 40, 1914, p. 131.
Leptynite, Hauy, 1822. A term applied to felspathic
granulites which differ from halleflintas in having
a coarser grain.
Lcptynolite, Cordier, 1868. A fissile or schistose
variety of hornfels containing mica, quartz and fel-
spar, with or without minerals such as andalusite
and cordierite. Cf. Cornubianite.
A. Lacroix : Bull. Serv. Carte Geol. France, x, 1898, -p. 8.
J. S. Flett : Mem. Geol. Surv. (Padstow and Camelford),
1910, p. 72.
Lestiwarite, Brogger f 1898. A leucocratic micro-
syenite or syenite-aplite. (Lestiware, Finland.)
W. C. Brogger : Eru-ptivgest. Kristiania, iii, 1898, p. 209.
I4 o THE NOMENCLATURE OF PETROLOGY
Leucite-basalt, Zirkel, 1870. A basaltic rock essen-
tially composed of leucite, pyroxene and olivine.
Leucite-phonolite. According to Rosenbusch this is
a volcanic rock whose felsic minerals are leucite
and orthoclase, without nepheline. With the ad-
dition of nepheline (or nosean, etc.) the rock be-
comes a leucitophyre. It is preferable, however,
to follow Zirkel, who calls the latter leucite-phono-
lite, and the former, from which nepheline is ab-
Leucite Rocks. (References)
W. Cross: Am. Journ. Sci., iv, 1897, p. 115.
H. S. Washington: Carnegie Inst. Wash. Pub., 57, 1906;
Journ. Geol., xv, 1907, p. 257.
J. P. Iddings & E. W. Morley : Journ. Geol., xxiii, 1915,
A. Lacroix : C.R., clxvi, 1917, p. 486.
Leucite-Syenite. A felspathoidal syenite containing
leucite, or, more generally, pseudo-leucite, the
latter consisting mainly of orthoclase and
A. Lacroix : C.R., clxv, 1917, p. 1032.
Leucite-tephrite. -- A variety of tephrite containing
both leucite and nepheline, or nosean, etc. Cf.
Leucite-trachyte, ^. Rath. A volcanic rock contain-
ing leucite in addition to the constituents of
tracrlyte = leucit e phonolite of Rosenbusch.
Leucitite. A fine-grained or porphyritic rock, com-
posed essentially of leucite and pyroxene ; a
basaltic rock with leucite instead of plagioclase,
and free from olivine.
Leucitophyre, Coquand, 1857. A variety of leucite-
phonolite, containing leucite and nepheline, or
other soda felspathoid, with generally inconspicu-
ous felspar ; the characteristic mafic constituent is
segirine or aegirine-augite.
Leuco-. A prefix added to the names of rocks to in-
dicate a leucocratic character. Cf. Melano-.
THE NOMENCLATURE OF PETROLOGY 14)
LeuCOCratic, Brogger, 1894. A term applied to facies
of igneous rocks, or to members of a series of asso-
ciated rocks, which are abnormally poor in mafic
(dark and heavy) minerals relative to the normal or
average rock-type of the mass or series.
LeilCOphyre, Gilmbel. A variety of diabase contain-
ing saussuritised felspar, pale green and purple
pyroxenes, ilmenite and abundant chlorite.
LeUCOtephrite, Fouque & Michel-Levy, 1879. A
term for tephrites containing leucite, but free from
nepheline or other soda felspathoid. The form
leucitephrile is preferable, as leucotephrite sug-
gests a leucocratic tephrite.
Lherzite, Lacroix, 1917. -- A holomelanocratic rock
composed of brown hornblende and biotite, with a
little ilmenite and occasionally garnet. The
chemical composition indicates that it contains
potential nepheline and leucite, and that it is a
heteromorphic form of theralite.
A. Lacroix : C.R., clxv, 1917, p. 385.
Lherzolite, De la Metherie, 1797. A variety of peri-
do>tite containing both monoclinic and ortho-
rhombic pyroxenes in addition to olivine.
, (Lherz, Pyrenees.)
A. Lacroix : Nouv. Arch, du Mus. <THist. Nat., 3 Ser., vi,
Liebenerite-porphyry. An altered nepheline-porphyry
in which the phenocrysts of nepheline have been
replaced by a scaly sericitic aggregate.
Lignite. A general term applied to coal-like deposits
usually of post-Carboniferous age, the most recent
approaching peat and the oldest approximating
to bituminous coal. Lignite is distinguished from
brown coal by containing over 20 per cent, of
water, and from ordinary coal by the fact that an
.i 4 2 THE NOMENCLATURE OF PETROLOGY
aqueous solution of potassium hydroxide is without
effect on the latter, whereas it dissolves lignite in
part, giving a brown solution.
Mem. GeoL Surv. Spec. Rep., Mineral Resources of Great
Britain, vii, 1918.
Limburgite, Rosenbusch, 1872. A rock consisting of
phenocrysts of olivine and pyroxene in an alkali-
rich glassy base ; = Magma-basalt, = (chemically)
Nepheline-basalt (with glass in place of nepheline).
Lime-b9Stonite, Brogger, 1894. -- A variety of bos-
tonite containing a notable amount of actual or
normative anorthite in the plagioclase or pyroxene
W. C. Brogger : Q.J.G.S., 1, 1894, p. 23.
J. V. Elsden : Q.J.G.S., Ixi, 1905, p. 594.
Limestone. - - A general term for bedded rocks of
exogenetic origin, consisting predominantly of
J. G. Goodchild : GeoL Mag., 1890, p. 71.
E. W. Skeats : Bull. Mus. Com-p. Zool. Harvard, xlii, 1903,
E. Steidtmann : Journ. GeoL, xix, 1911, pp. 223, 392.
J. E. Carne & L. J. Jones : GeoL Surv. N.S.W., Min. Res.,
Limurite, Zirkel, 1879. A contact rock formed
between granite and calcareous rocks, char-
acterised by an abundance of axinite (over 50 per
cent.), and also containing diopside, actinolite,
zoisite, albite, quartz and pyrrhotite.
A. Lacroix : C.R., cxv, 1892, p. 739.
Lindoite, Brogger, 1894. A leucocratic variety of
solvsbergite. (Lindo Is., Christiania.)
W. C. Brogger : Eru-ptivgest. Kristiania, i, 1894, p. 133.
Linear Foliation. A term applied to foliation which
is due to the linear arrangement of lamellar and
prismatic minerals such as biotite and hornblende.
It is often associated with mullion or rodding struc-
ture where the foliation is itself parallel to the dip
and pitch of the parallel series of folds of which
THE NOMENCLATURE OF PETROLOGY 143
that structure is one of the outward expressions.
Cf. Mullion Structure.
Mem. Geol. Surv. (N.W. Highlands), 1907, pp. 97-8, 245-7,
and PL xlix, Figs, i & 2.
Linophyric, C.I.P.W., 1906. A term applied to
porphyritic rocks in which the phenocrysts are
arranged in lines or streaks.
Lion's Haunch Basalt, Teatt, 1888. A variety of the
Dunsapie type (q.v-) of the Scottish Carboniferous
basalts, characterised by the presence of glass, and
sometimes of biotite and analcite, in the ground-
J. S. Flett : Mem. Geol. Surv. Scot. (Edinburgh), 1910, p.
Li pa rite, Roth, 1861. A term synonymous with
Rhyolite (q.v.). (Lipari Is.)
Liquation. A process of differentiation in which two
immiscible liquids separate from their common
solution (e.g., from a magma). The term has also
been applied to the separation of residual liquid
from crystals already formed.
N. L. Bowen : Journ. Wash. Acad. Sci. } viii, 1918, p. 88.
F. F. Grout : Journ. Geol., xxvi, 1918, p. 657.
Listwanite, Rose. - - A schistose rock of yellowish-
green colour composed of various combinations of
the minerals quartz, dolomite, magnesite, talc,
an,d limonite. (Beresowsk, Urals.)
Litchfieldite, Bayley, 1892. A nepheline-syenite con-
taining albite and dark mica, and in some varieties
having cancrinite in addition to nepheline ; inter-
mediate in respect of its felspars between mariu-
polite (albite) and foyaite (orthoclase).
W. S. Bayley : Bull. Geol. Soc. Am., iii, 1892, p. 231.
R. A. Daly : Bull. Geol. Soc. Am., 1918.
LithlC Tuffs, Pirsson, 1915. Volcanic tuffs, in which
the most conspicuous elements are fragments of
rocks. Cf. crystal and vitric tuffs.
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191.
i 4 4 THE NOMENCLATURE OF PETROLOGY
Lithoidal. A term meaning " stone-like" applied to
compact aphanitic materials.
Lithoidite, v. Rirtthofen, 1860. A rhyolite without
phenocrysts, made up entirely of cryptocrystalline
Lithology. The study of rocks as based on the
megascopic observation of hand-specimens. In
its French usage the term is synonymous with
Lithophysae, v. Rickthofen, 1860. A term applied to
hollow spherulites, often radial and concentric in
structure, occurring in rhyolite, obsidian and allied
G. A. J. Cole : Q.J.G.S., xli, 1885, p. 162.
F. E. Wright : Butt. Geol. Soc. Am., xxvi, 1915, p. 255.
Lithosiderite, Brezina, 1885. A group name for
stony-iron meteorites belonging to the sub-groups
of siderophyre and pallasite. Cf. Siderolite.
Lit-par-lit Injection. A term used to designate the
intimate penetration of bedded, schistose or other
fissile formations by innumerable narrow sheets
and tongues of granitic magma = Leaf-by-leaf
T. O. Bosworth : Q.J.G.S., Ixvi, 1910, p. 380.
Load Metamorphism, Daly, 1911. A name for a
type of static metamorphism in which high tem-
perature has been a controlling influence, as well
as overhead pressure.
R. A. Daly : Bull. Geol. Soc. Am., 28, 1917, p. 400.
Loam. A detrital deposit containing nearly equal
proportions of sand, silt, and clay, these terms
referring to the grade-sizes of the particles. The
term has generally been used in a much wider
sense, the restricted definition here given having
emerged during recent years as a result of grading-
work for economic purposes.
Lode or Vein. General terms for epigenetic mineral
deposits, the form of which is characterised by
THE NOMENCLATURE OF PETROLOGY 145
small thickness in relation to depth and length.
In America the term vein is used in preference to
Lodranite, Meunier, 1882. - - A siderolitic meteorite
containing- crystals of olivine and bronzite in a
matrix of nickel-iron.
Loess. A widespread deposit of silt or marl extending
from Central Europe through the steppes of Asia.
It is a buff-coloured, porous, but coherent deposit
traversed by a network of narrow tubes represent-
ing the negatives of successive generations of
grass-roots. The comminution of the constituents
is ascribed to the grinding action of glaciers, the
fine grade and distribution to the action of wind,
and the accumulation in thick deposits to the grip
Longulites, Vogelsang, 1870. Elongated crystallites
of cylindrical or conical forms considered to be
formed by the adhesion of linear series of globu-
F. Rutley : Min. Mag., ix, 1891, p. 261.
Lopolith, Gvout, 1918. -- A large lenticular intrusive
body of igneous rock, generally concordant, and
differing from a sill by being centrally depressed,
so that its upper surface is basin-like.
F. F. Grout : Am. Journ. Sci., xlvi, 1918, p. 516.
Luciite, Chelius, 1892. A fine-grained variety of
diorite, composed essentially of plagioclase, horn-
blende, and in some varieties a little quartz. The
type differs from malchite only in its coarser grain.
Lugarite, Tyrrell, 1912. A porphyritic rock contain-
ing phenocrysts of titanaugite and barkevikite,
with small and variable amounts of labradorite, in
a base of analcite (with traces of nepheline) which
makes up about half of the rock.
G. W. Tyrreli : Q.J.G.S., Ixxii, 1917, p. 107.
Lujaurite, Brogger, iSgo-LujaVtite, Ramsay, 1894.
A variety of nepheline-syenite, with trachytoid
i 4 6 THE NOMENCLATURE OF PETROLOGY
texture, containing aegirine, and characterised by
the conspicuous presence of eudialyte.
(Lujaur Urt, Kola.)
W. Ramsay : Fennia, xv, 2, p. 3.
Ltindyite, Hall, 1914. An intrusive rock with ortho-
phyric texture characterised by a high percentage
of alkalies and the presence of a catophorite-like
amphibole. The rock has been, analysed, but not
described. (Lundy Is.)
Summ. Prog. GeoL Surv. (1914), 1915, pp. 53 & 56.
LllSCladite, Lacroix, 1920 A type of olivine-
theralite or essexite characterised by the general
absence of hornblende (cf. Berondrite), and the pre-
sence of olivine and often of biotite. Orthoclase
mantles the plagioclase, and nepheline, not abun-
dant, occurs interstitially. The Crawfordjohn
essexite is a British example, and kylite is a
(Ravin de Lusclade, Mont-Dore.)
A. Lacroix : C.R., clxx, 1920, p. 21.
Lusitanite, Lacroix, 1916. A mesocratic alkali-syenite
containing riebeckite and aegirine.
(Alter Pedroso, Portugal.)
A. Lacroix : C.R., clxiii, 1916, p. 279.
Llixullianite, Pisani, 1864. A variety of tourmalinised
granite, in which the tourmaline occurs as radiat-
ing sheaves of acicular crystals embedded in
quartz. (Luxulyan, Cornwall.)
T. G. Bonney : Min. Mag., i, 1877, p. 215.
J. S. Flett : Mem. Geol. Surv., 347 (Bodmin and St. Austell),
1909, p. 66.
Lydite. - - A siliceous rock of extremely fine grain,
composed essentially of quartz and chalcedony ;
usually grey-black, owing to carbonaceous matter ;
but sometimes brown or green, due to the presence
of iron hydroxides or chlorite respectively. Lydite
occurs as chert-like bands in the older formations,
where it represents silicified shales, limestones or
tuffs. = Lydian Stone.
THE NOMENCLATURE OF PETROLOGY 147
Macedonite, Skeats & Summers, 1909. An aphanitic
basaltic rock containing- minute felspars, nosean,
melilite, perovskite, and pseudomorphs after
olivine (serpentine or chlorite) in a green vitreous
or chloride base. (Mt. Macedon, Victoria.)
E. W. Skeats : Australian Ass. Ad. Sci. (1909), 1910, p. 173.
Geol. Surv. Victoria, Bull. No. 24, 1912.
Maculose, Holmes, 1919. A term suggested for a
group of contact-metamorphosed rocks, including
spotted " slates," knotenschiefer, and hornfels, to
connote their spotted, knotted, and gnarled struc-
tures. The term may be applied to either the rocks
or their structures, and serves to distinguish them
from those described as gneiss ose, granules e, and
schistose, into any of which maculose rocks and
structures may pass by the continued action of
more intense metamorphism. See Table on p. 280.
Madeirite, Gagel, 1912. - - A porphyritic variety of
alkali-picrite containing abundant phenocrysts of
titaniferous augite and somewhat serpentinised
olivine in a groundmass consisting mainly of
augite and magnetite with a little plagioclase.
C. Gagel : Zeit. Deutsch. Geol. Ges.s., Ixiv, 1912, p. 399, and
Madupite, Cross, 1897. A fine-grained rock, consist-
ing essentially of phenocrysts of diopside and
phlogopite in a ground mass of glass having
approximately the composition of leucite.
W. Cross : Am. Journ. Sci., iv, 1897, p. 139.
Maenaite, Brogger, 1894. A fine-grained holocrystal-
line rock intermediate in type between the mon-
zonitic felsites and the dioritic lamprophyres, and
characterised by an abundance of hornblende.
(Maena, South Norway.)
Mafic, C.I.P.W., 1912. A mnemonic term for the
ferromagnesian and other non-felsic minerals
actually present in an igneous rock, and also
L applied to rocks in which those minerals pre-
i 4 8 THE NOMENCLATURE OF PETROLOGY
dominate ; not synonymous with femic, which
refers to the normative constituents of a rock cal-
culated from its chemical analysis.
C.I.P.W. : Journ. Geol., xx, 1912, p. 561.
Mafraite, Lacroix, 1920. A heteromorphic form of
berondrite containing- soda-hornblende in large
idiomorphic crystals, together with pyroxene and
labradorite. The type differs from berondrite by
the absence of nepheline, the constituents of that
mineral being- present in the amphibole.
(Mafra, Cintra, Portugal.)
Magma. A comprehensive term for the molten fluids
generated within the earth from which igneous
rocks are considered to have been derived by
crystallisation or other processes of consolidation.
A magma includes not only the material repre-
sented by all or part of an igneous rock, but also
any volatile fluxes and residual liquors which may
have escaped during or after consolidation. It is
therefore not correct to assume that the composi-
tion of a rock represents that of the magma from
which it developed. In the case of suddenly
chilled margins this may except for gases and
vapours be nearly true, but where the rocks of
an area reveal differentiation into a wide range of
types, these types may represent chemically only
fractions of the bulk-magma, and from the latter
therefore they may differ very considerably.
Magma-basalt, Boricky, 1872. A term in part synony-
mous with Limburgite (q.v.), but also applied to
porphyritic, glassy basaltic rocks more closely re-
lated to ordinary basalt.
Magmatic Assimilation. See Assimilation.
Magmatic Stoping, Daly, 1906. A process whereby
rock magmas are enabled to take the place pre-
viously occupied by pre-existing rocks, involving
(i) marginal shattering of the rocks along the roof
and walls of the magmatic chamber ; and (2) sink-
THE NOMENCLATURE OF PETROLOGY 149
ing of the blocks and fragments so produced, with
concomitant occupation of the space so liberated,
by lateral or upward movement of the magma.
R. A. Daly : Ig. Rocks and their Origin, New York, 1914,
Magnesian Limestone. In its petrological usage (as
opposed to its stratigraphical application to a Per-
mian formation) this term has been given to lime-
stones containing MgCO 3 (about 5 to 15 per cent.),
but in which dolomite cannot be detected either
optically, or by the Lemberg reaction. Such
rocks are thus distinguished from Dolomitic Lime-
stone, in which dolomite is demonstrably present
in addition to calcite. The connotation of mag-
nesian limestone is, however, generally interpreted
more widely, especially as a field-term.
R. C. Wallace : Cong. Geol. Inter,, C.R. xii (1913), 1914,
D. \Voolacott : Geol. Mag., 1919, pp. 452 and 485.
Magnesite Rock. A carbonate rock consisting pre-
dominantly of the mineral magnesite.
T. Crook : Trans. Ceramic Soc., 1919, p. 67.
Magnetite-hogbomitite, Gavelin, 1917. A rock com-
posed of numerous crystals of grey hogbomite, and
occasional flakes of white hydrargillite, in a black
magnetite-ilmenite matrix. Hogbomite is a
mineral having the composition RO.2R 2 O 3 where
RO is mainly MgO, and R 2 O 3 is mainly A1 2 O 3 and
Fe 2 O 3 , together with a certain amount of TiO 2 .
A. Gavelin : Bull. Geol. Inst. U-psala, xv, 1917, p. 310.
Magnetite-olivinite, Sjogren, 1876. A variety of
dunite rich in titaniferous magnetite and contain-
ing shreds of biotite. (Taberg, Sweden.)
Magnophyric, C.I.P.W., 1906. A term applied to
coarsely porphyritic rocks with phenocrysts ex-
ceeding 5 mm. in one or more of their dimensions.
Malchite, Osann, 1892. A term applied to rocks
which have been described asi micro-diorite, or
ISO THE NOMENCLATURE OF PETROLOGY .
diorite-felsite, and which differ from porphyrite by
the absence of conspicuous phenocrysts.
Mem. Geol. Surf. Scotland (Glen Coe), 1916, pp. 156, 175.
Malignite, Laws on, 1896.- A melanocratic variety of
nepheline-syenite. (Maligne R., California.)
A. C. Lawpon : Bull. De-pt. Geol. Univ. California, Pub. i,
1896, p. 337.
R. A. Daly : Bull. Geol. Soc. Am., 1906, xvii, p. 329.
Manganolite, Wadsworth, 1891. A general term pro-
posed for rocks composed of manganese-minerals.
Mangerite, Kolderup, 1903. A variety of monzonite.
(Manger, near Bergen.)
C. F. Kolderup : Bergen Mus. Aarbeit., No. 12, 1903, p. 107.
Manjak. A black variety of bitumen, having a bril-
liant lustre and conchoidal fracture; H about 2;
S.G. = 1.06-1.07. (Barbados.)
Marble. A general term for any calcareous or other
rock of similar hardness that can be polished for
decorative purposes ; petrologically restricted to
granular crystalline limestones, the term, when
used without a mineralogical prefix, implies a
variety such as statuary marble, composed almost
entirely of calcite.
Marekanite. A variety of perlitic rhyolite-glass from
which large perlitic masses of clear glass readily
separate. (Marekana, Okhotsk, Siberia.)
J. W. Judd : Geol. Mag., 1886, p. 241.
K. Bogdanovitch : Fundort des Marekanits, St. Petersbourg,
Mareugite, Lacroix, 1917. An even-grained theralitic
rock, consisting of bytownite and hauyne with
variable and sometimes considerable amounts of
hornblende and augite. (Mareuge, Auvergne.)
A. Lacroix : C.R., clxiv, 1917, p. 587.
Margarite, Vogelsang, 1872. An aggregate of globu-
lites, or minute sphere-like crystallites, arranged
like beads in a linear series.
F. Rutley : Min. Mag., ix, 1891, p. 261.
THE NOMENCLATURE OF PETROLOGY 151
Margination Texture, Plolmquist, 1906. A texture
due to magmatic corrosion phenomena in granites ;
characterised by curved and sinuous contacts be-
tween quartz and felspar, the material of later
crystallisation having corroded the mineral already
P. J. Holmquist : Bull. Geol. Inst. U-psala, vii, 1906, p. 116.
Mariupolite, Morozewicz, 1902. An albite-nepheline-
syenite of variable grain, containing segirine and
lepedomelane, with zircon and beckelite as notable
accessories. (Mariupol, Sea of Azov.)
Markfieldite, Hatch, 1909. --An igneous rock com-
posed of idiomorphic crystals of plagioclase, to-
gether with augite and/ or hornblende, embedded
in a gro'undmass of micropegmatite. The term
thus denotes a dioritic granophyre, intermediate
between granophyre and granodolerite.
(Markfield, Charnwood Forest.)
Markle Basalt, Hatch, 1892. A type of the Scottish
Carboniferous basalts ; characterised by the pre-
sence of large and numerous phenocrysts of labra-
dorite with small grains of olivine in a normal
basaltic groundmass. The type differs from the
Jedburgh type in being much more conspicuously
E. B. Bailey : Mem. Geol. Surv. Scot. (East Lothian), 1910,
G. W. Tyrrell : Trans. Geol. Soc. Glasgow t xiv, 1912, p. 241.
Marl. A general term for calcareous clay or calcare-
Marloesite, Thomas, 1911. A rock somewhat re-
sembling pantellerite, containing glomero-por-
phyritic groups of olivine and albite-oligoclase in a
felted! ground mass composed largely of soda-
felspar. (Marloes, Skomer Is., Pembroke.)
H. H. Thomas : Q.J.G.S., Ixvii, 1911, p. 175.
152 THE NOMENCLATURE OF PETROLOGY
Marosite, Iddings, 1913. A variety of shonkinite con-
taining- augite and biotite, with subordinate alkali-
felspar and felspathoid. (Pic de Maros, Celebes.)
J. P. Iddings & E. W. Morley : Journ. Geol., xxiii, 1915, p.
Marscoite, Harker, 1904. A hybrid rock, due to the
partial absorption of granitic material by a gabbro
magma, containing xenocrysts of quartz and
felspar in a gabbroid matrix of abnormal composi-
tion. The name is intended for local use only, and
not to connote a new rock-type. (Marsco, Skye.)
A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904,
pp. 175, 186.
Masanite, Koto, 1909. A variety of quartz-monzonite-
porphyry having phenocrysts of zoned plagioclase
and corroded quartz in a finely granitic or micro-
pegmatitic groundmass. (Ma-san-po, Korea.)
Masanophyre, Koto, 1909. A variety of masanite in
which the felspar phenocrysts consist of oligoclase
mantled with orthoclase, and of which the ground-
mass contains blue-green hornblende, and sphene.
B. Koto : Journ. Col. Sci., Tokyo, xxvi, 1909, p. 189.
Mediophyric, C.I.P.W., 1906. -- A term applied to
porphyritic rocks with phenocrysts between 5 mm.
and i mm. in their longest dimensions.
Mediosilicic, Clarke, 1911. A term suggested in place
of "intermediate" to connote that the rocks so
described have a silica-content falling between 52
and 66 per cent.
Megascopic. A general term, more appropriate than
macroscopic, applied to observations made on
minerals and rocks, and to the characters
observed, by means of the naked eye or pocket-
lens, but not with a microscope.
Meigen's Reaction. A test for the discrimination of
calcite and aragonite. A solution of cobalt nitrate
is used as a combined stain and reagent.
Aragonite is stained to a lilac tint which remains
visible in thin section, after boiling with the solu-
THE NOMENCLATURE OF PETROLOGY 153
tion for about twenty minutes ; calcite (and dolo-
mite) may be stained pale blue, but appear un-
changed in thin section.
Melanocratic, Brogger, 1894. - - A term applied to
rocks, or to members of a series of associated
rocks, which are abnormally rich in mafic (dark
and heavy) minerals relative to the normal or
average* rock-type of the mass or series.
Melano-, Mela-. Prefixes added to the names of rocks
to indicate a melanocratic character. Cf. Leuco-.
Melaphyre, Brohgniairt, 1813. A general term for
altered and amygdaloidal rocks of basaltic or
B. von Cotta : Rocks Classified and Described, trans, by P.
H. Lawrence, 1878, p. 154.
Melilite-basalt, v. Rath, 1866. A highly under-
saturated basaltic rock essentially containing
augite, melilite, and olivine. Nepheline is fre-
quently present, and perovskite and spinellids are
A. VV. Rogers & A. L. Du Toit : Trans. S. Af. Phil. Soc.,
xv, 1904, p. 61.
G. T. Prior : Min. Mag., 1903, p. 228.
Melilitite, Lacroix, 1896. An igneous rock essentially
composed of melilite and pyroxene. Nepheline-
and leucite-melilitites are distinguished ; and by the
introduction of olivine the rocks become meliHte-
basalts. When the felspathoid minerals are
dominant the terms melilite-nephelinite , or -leucitite
may be used ; and when olivine is also present,
melilite-nepheline-basalt, or -leucite-basalt..
A. Lacroix : Min. de la France, ii, 1896, p. 501.
Merocrystalline. = Hemicrystalline.
MeSO-, Grubenmann, 1907. A prefix used as a quali-
fier to the group-names suggested by Grubenmann
for metamorphic rocks, to indicate that the type so
distinguished belongs to the " middle zone " of
metamorphism. In this zone the distinctive
154 THE NOMENCLATURE OF PETROLOGY
physical conditions are high temperature and
hydrostatic pressure and intense stress, and the
rocks characteristically produced include mica-
schists, garnetiferous and staurolite-schists, horn-
blende-schists, amphibolite and various types of
crystalline limestones, quartzites and gneisses.
Cf. Epi-, and Kata-.
U. Grubenmann : Die Kristallinen Schiefer, II, 1907, pp.
MeSOCratic. - - A term applied to facies of igneous
rocks, or to members of a series of associated
rocks, which are somewhat richer in mafic (dark
and heavy) minerals than the normal or average
rock-type of the mass or series, but not suffi-
ciently rich to be called melanocratic.
MeSOSiderite, Rose, 1864. A general terrn^ for
achondritic meteorites in which both silicate-
minerals and nickel-iron are present in large pro-
portions ; = Siderolite.
MeSOStasis. A term applied to the ultimate inter-
stitial material of a rock which consolidated in the
final stage of solidification as a glass (e.g., in in-
tersertal basalts), a single mineral (e.g., analcite,
in teschenite), or a eutectic (e.g., micropegmatite,
Meta-. A prefix used before the names of igneous
rocks to signify that the mineral and chemical com-
position of the latter have been modified by altera-
Metabasite, Hackman, 1907. A general term for
metamorphosed basaltic, doleritic and allied rocks,
the types included ranging from diabase and
epidiorite to hornblende-schist.
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 23, 1907,
Metabolite, Wadsworth, 1891. A term proposed for
altered trachyte-glass, the fresh rock being
described as lassenite.
THE NOMENCLATURE OF PETROLOGY 155
Metacrystal, Lane, 1902. A term applied to the large,
pseudoporphyritic crystals, such as staurolite and
garnet, in metamorphic rocks ; == Porphyroblast.
A. C. Lane : Bull. Geol. Soc. Am., xiv, 1902, p. 386.
Metallogeny. - - The genetic study of ore-deposits in
relation to age, regional tectonics, and petro-
graphic provinces. Metallogenic provinces and
epochs are recognised.
A. M. Finlayson : Q.J.G.S., Ixvi, 1910, p. 281.
C. Iwaski : Journ. Col. Sci. Tokyo, xxxii, 1912, No. 8.
W. G. Miller & C. W. Knight : Trans. Roy. Soc. Canada,
ix, 1915, p. 241.
L. L. Fermor : Proc. Asiatic Soc. Bengal, xv, 1919, p. clxx.
Metamorphic Differentiation, Stillwell, 1918. -- The
segregation into definite minerals of materials which
has migrated from other parts of the rocks con-
cerned by metamorphic diffusion (see below).
F. L. Stillwell : Aust. Ant. ' Ex$ed. Sci. Re-p. A, iii,
i (i) (Met. Rocks, Adelie Land), 1918, p. 72.
Metamorphic Diffusion, Stillwell, 1918. The migra-
tion by diffusion of material from one part of a
rock to another during its recrystallisation.
F. L. Stillwell : Aust. Ant. Escaped. Sci. Rep. A, iii,
i (i) igiS, (Adelie Land and critical discussion).
Metamorphic Rocks. Rocks derived from pre-exist-
ing rocks by mineralogical, chemical, and
structural alterations due to endogenetic pro-
cesses ; the alteration having been sufficiently
complete throughout the body of the rock to have
produced a well-defined new type. (For references
see below, p. 156.)
Metamorphism, Lyell, 1833. The sum of the thermo-
dynamic processes of endogenetic origin which
cause the transformation of a rock into a well
characterised new type by more or less thorough
recrystallisation, and change of texture and
structure, with or without the introduction of new
material. By some authors (Van Rise, Leith &
Mead, et alitcr) metamorphism is defined so as to
156 THE NOMENCLATURE OF PETROLOGY
include all the changes in rocks after their crystal-
lisation from magmas. This extreme overburden-
ing of the term makes it synonymous with altera-
tion, and thereby renders it useless. Disregard-
ing the etymology of the word, it is expedient to
restrict its significance to endogenetic alterations
as denned above. A full account of the varied
usage is to be found in the paper by Daly referred
G. Barrow : Q.J.G.S., xlix, 1893, p. 330.
F. Becke : Cong. Geol. Inter., C.R. ix. 1903, p. 553 (Mine-
rals and Structures).
C. R. Van Hise : U.S.G.S., Mon., 47, 1904 (General).
Mem. Geol. Surv. (N.W. Highlands), 1907.
E. S. Bastin : Journ. Geol., xvii, 1909, p. 449; and xi, 1913,
p. 193 (Criteria of origin).
U. Grubenmann : Die Kristallincn Schiefer, Berlin, 1910.
V. M. Goldschmidt : Die Kontactmetamor-pJwse im Kris-
Mem. Geol. Surv., 359 (Lizard), 1912.
J. D. Truemann : Journ. Geol., xx, 1912, p. 236 (Criteria of
L. Milch : Journ. Geol., xx, 1912, p. 272.
J. Johnston & P. Niggli : Journ. Geol. xxi, 1913, p. 610
C. K. Leith & W. J. Mead : Metamor-phic Geology, 1915.
R. A. Daly : Bull. Geol. Soc. Am., xxviii, 1917, p. 375
(Classifications and Definitions).
A. Harker : Q.J .G.S., Ixxiv, 1918, p. Ixiii (General review).
J. J. H. Teall : Proc. Geol. Assoc., xxix, 1918, p. i (Dyna-
W. Lindgren : Journ. Geol., xxvi, 1918, p. 542 (Volume
F. L. Stillwell : Aust. Antarc. Ex-ped. Set. Re-p., Vol. A,
iii, i (T) 1918, (Adelie Land and critical discussion).
T. G. Bonney : Geol. Mag., 1919, pp. 196, 246 (Foliation).
Metasomatism, Naumann. - - The processes by which
one mineral is replaced by another of different
chemical composition owing to reactions set up by
the introduction of material from external sources.
Metasomatic rocks are those whose chemical com-
position has been substantially changed by the
metasomatic alteration of its original constituents.
W. Lindgren : Econ. Geol., vii, 1912, p. 521 ; Journ Geol.,
xxvi, 1918, p. 543.
THE NOMENCLATURE OF PETROLOGY 157
Metastable, Os timid t 1897. - - A term describing- the
condition of a supersaturated solution in which the
presence of the .solid phase is necessary to stimu-
late the separation of the solute.
H. A. Miers : Trans. Chem. Soc., Ixxxix, 1906, p. 427.
Meteorite. A general term for mineral aggregates of
cosmic origin that reach the earth by falling
through the atmosphere from interplanetary space.
O. C. Farringdon : Journ. Geol., ix, 1911, p. 51, etc.
G. T. Prior : Min. Mag., xviii, 1916, p. 26.
Miaskite, Rose, 1839. A variety of nepheline-syenite
containing biotite as the chief mafic constituent.
, (Miask, Urals.)
Mica-Schist. A schist composed essentially of micas
and quartz, the foliation being mainly due to the
parallel disposition of the mica-flakes. Quartz
may be granular or lenticular. Many varieties are
recognised, such as those containing garnet or
staurolite, in addition to the group minerals, and
are distinguished by the use of prefixes specifying
the chief varietal mineral.
Micro-. A prefix commonly added (i) to the names
of megascopic textures to indicate a texture of
similar type developed on a microscopic scale ;
e.^., microgranitic, micrographic, micro-
Doikilitic, etc. ; (2) to the names of phanerocrystal-
line rocks to indicate a microcrystalline rock or
groundmass of corresponding mineral composi-
tion and texture; e.g., microgranite, micro-
diorite, microsyenite, etc.
Microcrystalline. A term applied to a rock or ground-
mass in which the individual crystals can only be
seen as such under the microscope.
Micrplites. -- A general term for minute crystals of
tabular or prismatic habit, occurring in micro-
crystalline or hemicrystalline rocks and ground-
masses. Microlites are distinguished from crystal-
lites by their capacity to give a reaction with
158 THE NOMENCLATURE OF PETROLOGY
Microlitic Texture, Fouque & Michel Levy. The tex-
ture of a porphyritic rock having a microcrystal-
line groundmass composed largely of more or less
idiomorphic tabular or prismatic crystals (e.g. ,
felspar laths) with or without interstitial glass.
Micropegmatite, Michel Levy, 1896. - - A term for
micrographic aggregates of quartz and felspar
occurring as a gro mdmass or mesostasis in vari-
ous igneous rocks.
T. H. Holland : Q.J.G.S., liii, 1897, p. 405.
W. Mackie : Trans. Edin. Geol. Soc., ix, 1909, p. 247.
S. J. Schofield : Geol. Surv. Canada Mus. Bull., 2 (Geol.
Series No. 13), 1914.
N. L. Bowen : Journ. Geol. Su-p-p. Vol., xxiii, 1915, p. 17.
Microtinite, Lacroix 1901. A coarse-grained leuco-
cratic rock of monzonitic or dioritic texture con-
taining vitreous plagioclase (microtinite). The
type occurs as enclaves homceogenes in lavas.
(Roc Blanc, Auvergne.)
A. Lacroix : C.R., cxxxi, 1900, p. 348.
Migmatite, Sederholm, 1907. A term applied to com-
posite rocks, such as gneisses, produced by the
injection of granitic magma between the folise of
a schistose formation. Cf. Composite gneiss.
J. J. Sederholm : Bull. Comm. Geol. Finlande, 23, 1907, p.
Miharaite, Tsuboi, 1918. A variety of basalt char-
acterised by abundant phenocrvsts of bytownite
and fewer of pyroxenes in an intersertal ground-
mass containing occult free silica ; = bytownite-
tholeiite. Cf. Cumbraite.
Seitaro Tsuboi : Jonrn. Geol. Soc., Tokyo, xxv, 1918, p. 47.
Mijakite, Peter sen ^ 1891. -- A red-brown porphyritic
variety of basalt, containing phenocrysts of bvtow-
nite and augite in a groundmass containing
plagfioclase, magnetite, manganese-pyroxene and
glass. (Mijakeshima, Japan.)
Miliolite, Carter, 1849. A fine-grained limestone of
?eolian origin occurring in Kathiawar, and con-
THE NOMENCLATURE OF PETROLOGY 159
sisting of the tests of Miliolina and other foramini-
fera, oolitic grains, and mineral fragments,
cemented by calcite.
J. W. Evans : Q.J.G.S., Ivi, 1900, p. 559.
Mimosite, Cordier, 1868. - - A melanocratic dolerite
rich in augite and ilmenite. Cf. Soggendalite.
Mineralisers. -- A term applied to magmatic gases,
such as hydrogen, water and compounds ol
fluorine, boron, sulphur, carbon, etc., and other
volatile substances, which
(i) by lowering viscosity, extending the tem-
perature range of crystallisation, and acting as
catalytic agents, are able to facilitate the crystal-
lisation of various minerals ; (2) enter into the
composition of certain minerals which could not
otherwise be formed ; and (3) are capable of ex-
tracting and concentrating metallic and other
compounds from the magma through which they
were originally dispersed. = Agents mineralisa-
A. Marker : Nat. Hist. Ig. Rocks, 1909, p. 282.
W. H. Goodchild : Mining Mag., xviii, 1917, p. 190; xix,
1918, p. 189.
Minette, Voltz, 1822. A syenitic lamprophyre com-
posed essentially of biotite and orthoclase. The
term was originally and still is> applied to the Jur-
assic ironstones of the Briey basin and Lorraine.
Minette-felsite, Bonney & Haughton, 1879. A term
proposed for minette-like rocks having a micro- or
crypto-crystalline groundmass : minette proper
having a finely phanerocrystalline groundmass.
T. G. Bonney : Q.J.G.S., xxxv, 1879, p. 166.
Minophyric, C.I.P.W., 1906. - - A term applied to
porphyritic rocks with phenocrysts between
i mm. and 0.2 mm. in their longest dimensions;
"phenocrysts " smaller than these are microlites.
" Minus " Minerals, Lcewinson - Lessing, 1897. -
Minerals (such as garnets) whose molecular
volumes are less than the sum of the molecular
160 THE NOMENCLATURE OF PETROLOGY
volumes of the constituent oxides. In the case of
allotropic modifications of the latter, the more con-
densed form, having the smaller molecular volume,
is assumed for the calculation.
F. Loewirjson-Lessing : Cong. Geol. Inter., C.R. vii, 1897,
W. H. Goodchild : Mining Mag., xviii, 1917, pp. 243, 298.
Minverite, Dewey, 1910. A proterobase, containing
primary brown hornblende, purple-brown augite
and albitised felspars; the type differs from albitc-
diabase in the possession of primary hornblende.
(St. Minver, N. Cornwall.)
H. Dewey & J. S. Flett : Geol. Mag., 1911, p. 207.
Mem. Geol. Surv., 335-6 (Padstow), 1910, p. 46.
MisSOUrite, Weed & Pirsson, 1896. A phanero-
crystalline rock, containing pyroxene, leucite, and
olivine, and consequently the plutonic equivalent of
a leucite-basalt. (Missouri.)
W. H. Weed & L. V. Pirsson : Am. Journ. Sci., ii, 1896,
Mix-Crystal. A general term for crystals composed of
two or more isomorphous or partly isomorphous
constituents; e.g., plagiocla.se felspars (NaAlSi,O a
and CaAl 2 Si 2 O 8 ), hypersthene (MgSiO 3 and
FeSiO 3 ), etc.
Mode, C.I.P.W., 1902. The actual mineral composi-
tion of a rock expressed quantitatively in percent-
ages by weight, as opposed to the norm (q.v.).
Moldavites. A term for the green obsidianites which
occur as rolled pebbles in certain of the valleys of
Bohemia. Their origin is obscure, but is almost
certainly extra-terrestrial. (Moldau, Bohemia.)
F. E. Wright : Bull. Geol. Soc. Am:, xxvi, 1915, p. 280.
Molecular Proportion. The figure obtained for any
constituent of a rock or mineral by dividing its
percentage by its molecular weight. The alter-
native term Molecular Number proposed by
Washington is already applied to the sum of the
atomic numbers of the atoms in a molecule of any
THE NOMENCLATURE OF PETROLOGY 161
compound, and is therefore not suitable for the
purpose intended by Washington. For tables of
molecular proportions see
C.I.P.W. : Quantitative Classification of Igneous Rocks,
H. S. Washington : U.S.G.S. Prof. Pa-p., 1917.
J. F. Kemp : Handbook of Rocks, 1918, p. 171 et seq.
A. Holmes : Petro graphic Methods and Calculations, 1920.
Molecular Volume. The figure obtained by dividing
the molecular weight of any substance by its
specific gravity ; = Solid specific volume.
W. H. Goodchild : Mining Mag., xviii, 1917, pp. 243, 298;
xix, 1918, p. 84.
Monchiquite, Rosenbusch &* Hunter, 1890. -- A
melanocratic dyke rock, microcrystalline or
porphyritic, containing abundant mafic minerals,
with little or. no felspar, in an isotropic base,
which consists, or has the composition, of anal-
cite. Most examples contain olivine, and nep-
heline- and leucite-bearing varieties are recognised.
(Serra de Monchique, Portugal.)
J. W. Evans : Q.J.G.S., Ivii, 1901, p. 38.
Mem. Geol. Surv. Scot. (East Lothian), 1910, p. 107.
A. Holmes : Geol. Mag., 1915, p. 324.
Mondhaldeite, Graeff, 1900. A dyke rock of mon-
zonitic composition containing phenocrysts of
augite, hornblende, bytownite and leucite in a
glassy base. (Mondhalde, Kaiserstuhl, Baden.)
Monmouthite, Adams, 1904. -- A phanerocrystalline
rock composed essentially of nepheline (about 70
per cent.) and hornblende (hastingsite) with acces-
sory albite, cancrinite and calcite.
(Mon mouth Co., Ontario.)
F. D. Adams : Am. Journ. Sci., xvii, 1904, p. 269.
Monotropic. A term applied to the transition from
one polymorphic form of a substance to another
(e.g., MgSiO 3 as amphibole -> MgSiO 3 as mono-
clinic pyroxene) when the change can take place
only in one direction. It is possible, however,
162 THE NOMENCLATURE OF PETROLOGY
that monotropic processes may be so limited only
when the action of shearing- stress is left out of
Moiltrealite, Adams, 1913. -- A highly melanocratic
variety of olivine-essexite. (Montreal.)
F. D. Adams : Cong. Geol. Inter., C.R. xii, Guide, 3, 1913,
Monzonite, de Lapparent, 1864. A phanerocrystal-
line rock, having approximately equal quantities
of orthoclase and plagioclase, so that the rock is
intermediate between syenite and diorite, or
syenite and gabbro. It is desirable that the
plagioclase should be at least as calcic as labra-
dorite, and that rocks intermediate between syenite
and diorite should be distinguished as syenodiorite,
monzodiorite or orthoclase-diorite.
W. C. Brogger : Ern-ptivgest. Kristiania, ii, 1895, p. 6.
Monzonitic Texture. A texture characterised by the
idiomorphism of plagioclase crystals with ortho-
clase occupying part of the interstitial spaces.
Mortar Structure. A mechanical structure in which
small grains produced by granulation occupy the
cracks or interstices between larger individuals.
Mosaic Texture. A granulose texture of meta-
morphic rocks in which the individual grains meet
with nearly straight or but slightly curved con-
tacts ; = Gran oblas tic.
Mud Cracks. A general term for the irregular desic-
cation fractures, crudely simulating a series of
polygons, formed in the superficial layers of a
deposit of mud exposed to the atmosphere.
E. M. Kindle : 'fourn. Geol., xxv, 1917, p. 135.
Mudstone. An indurated non-laminated sediment
composed of clay-minerals and other constituents
of the mud grade. Cf. Shale.
Mugearite, Harker, 1904. -- A dark finely-crystalline
rock of trachytic to loasaltic aspect, distinguished
from basalt by the occurrence of oligoclase and
orthoclase in place of labradorite, by generally con-
THE NOMENCLATURE OF PETROLOGY 163
taining- olivine in greater amount than augite, and
by the possession of a trachytic rather than a
basaltic texture. (Mugeary, Skye.)
A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904,
J. S. Flett : Summ. Prog. Geol. Surv. for 1907, 1908, p. 119.
Mullion Structure, Kinahan, 1891. A structure first
observed in the folded metamorphic rocks of
Donegal, recalling the appearance of the clustered
columns which support the arches, or divide the
lights of mullioned windows, in Gothic churches.
The structure is also described as Rodding Struc-
ture, and is typically displayed in the Eirebol dis-
trict, where "rods" of white quartz, varying in
dimensions from those of telegraph poles to those of
walking sticks, lie parallel to each other down the
dip slope of the Moine schists. Where minerals of
elongated habit like hornblende and biotite are
present in the rocks showing mullion or rodding
structure the crystals are arranged parallel to each
other and to the dip and pitch of the folds. Cf.
Mem. Geol. Surv. (N.W. Highlands), 1907, pp. 97-8, 245-7,
and PI. xxv, facing p. 200.
See also Geol. Mag., 1871, p. 559, fig. 2, where mullion
structure is wrongly described as " ice-fluting."
Multiple (Intrusions). A term applied to sills, dykes,
laccoliths and other intrusions, formed by two or
more successive injections of approximately the
Mimipngite, David ct aliter, 1901. A variety of
tinguaite, containing about 44 per cent, of alkali-
felspar, 36 per cent, of nepheline and 20 per cent,
of aegirine-augite. (Kosciusko, N.S.W.)
T. E. W. David (et aliter} : Proc. Roy. Soc., N.S.W., xxxv,
1901, p. 366:
Murasakite, Koto, 1887. A schistose rock composed
essentially of piedmontite and quartz.
13. Koto: Journ. Coll. Sci. Univ. Japan, i, 1887, p. 303; ii,
1888, p. 94.
1 64 THE NOMENCLATURE OF PETROLOGY
Murbruk Structure. See Mortar Structure.
MuSCOVadite, Winchell, 1900. --An endomorphic
variety of norite characterised by the presence of
cordierite and biotite.
A. N. Winchell : Amer. Geol., xxvi, 1900, p. 294.
Mylonite, Lapiuorth 1885. A compact chert-like
rock, without cleavage, but with a streaky or
banded structure ; produced W the extreme granu-
lation and shearing of rocks which have been
pulverised and rolled out during overthrusting, or
by the action of dynamic metamorphism generally.
P. Quensel : Bull. Geol. Inst. Uppsala, xv, 1916, p. 91.
J. J. H. Teall : Proc. Geol. Assoc., xxix, 1918, p. 2 and
Mylonite-gneisS, Quensel, 1916. A rock partly granu-
lated and partly recrystallised, intermediate in its
characters between mylonite and schist. The
felsic minerals show cataclastic phenomena with-
out much recrystallisation, and often occur in
aggregates as " augen " surrounded by and alter-
nating with schistose streaks and lenticles of the
recrystallised dark or mafic minerals ; = Augen-
P. Quensel : Bull. Geol. Inst. U-psala, xv, 1916, p. 101.
Myrmekite, Sederholm, 1899. An intergrowth of
plagioclase and vermicular quartz, generally re-
placing potash felspars, formed during the later
or paulopost stages of consolidation, or during a
subsequent period of plutonic activity.
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916,
Nakhlite. An achondritic meteoritic stone consisting
of a holocrystalline aggregate of diopside, and
olivine, with a little interstitial oligoclase, augite
G. T. Prior : Min. Mag., xvi, 1912, p. 274.
Napoleonite. See Corsite.
THE NOMENCLATURE OF PETROLOGY 165
Naujaite, Ussing, 1911. A variety of nepheline-
sodalite-syenite rich in sodalite, and also contain-
ing microcline and small amounts of albite,
analcite, aegirine and soda-amphiboles ; char-
acterised by a peculiar poikilitic texture.
(Naujakasik, Illimausak, S. Greenland.)
N. V. Ussing : Medd. om Gronland, xxxviii, 1911, p. 154.
Navite, Rosenbusch, 1887. A porphyritic variety of
olivine-dolerite, containing abundant phenocrysts
of serpentinised olivine, with fewer of augite and
labradorite, in a holocrystalline doleritic ground-
mass. (Nave, Nahe Valley, Prussia.)
Neck. A vertical plug-like body of igneous rock or
volcanic ejectamenta, or both, representing the
feeding channel of a volcano. = Vent.
Nelsonite, Watson, 1907. A dyke rock composed
essentially of ilmenite and apatite, and generally
. containing rutile. (Nelson, Virginia.)
T. L. Watson & S. Taber, : Bull. Geol. Surv. Virginia, iii,
Nematoblastic, Becke, 1903. A metamorphic texture
due to the development during recrystallisation of
minerals like sillimanite, having a fibrous habit.
Nepheline-basalt, Gerard, 1841. An undersaturated
basaltic rock essentially containing nepheline,
pyroxene, and olivine, with little or no felspar.
Nepheline-Syenite. -- A phanerocrystalline igneous
rock generally of granular or trachytoid texture,
composed essentially of alkali-felspars, nepheline,
and mafic minerals. The latter usually, but not
necessarily, include soda-pyroxenes and amphi-
boles ; other soda-felspathoids may be present in
addition to nepheline, and accessory minerals
such as zircon, sphene, apatite and others of rarer
occurrence, are often more than usually abundant.
A. Lacroix : Nouv. Arch., Mus. cTHist. N at., iv, 1902, p.
F. D. Adamp & A. E. Barlow : Mem. Geol. Surv. Canada,
No. 6 (Pub. 1082), 1910, p. 227.
P. Quensel : Bull. Geol. Inst. U-psala, xii, 1913, p. 163.
166 THE NOMENCLATURE OF PETROLOGY
Nephelinite, Cordier, 1868. - - An aphanitic or por-
phyritic rock composed essentially of augite and
nepheline, olivine being- -bsent. If the latter
mineral be present the rock is termed nepheline-
Nephelitlitoid Phonolite. A general term for phono-
lites in which felspathoids are more abundant than
Nevadite, v. Richthofen, 1868. A porphyritic variety
of rhyolite rich in phenocrysts. (Nevada.)
Newlandite, Bouncy, 1899. -- A variety of griquaite
composed of garnet, enstatite, and chrome-
diopside. (Xewlands Diamond Pipe, S. Africa.)
T. G. Bonney : Nat. Sci., xv, 1899, p. 177.
Nodule. A general term for concretionary bodies,
which can be separated as discrete masses from
the formation in which they occur.
G. F. Becker : U.S.G.S., Man. xiii, 1888, p. 64.
Nonesite, Lepsius, 1878. - - A variety of porphyritic
basalt characterised by phenocrysts of labradorite,
augite, and enstatite, in a groundmass of plagio-
clase and augite. (Near Mte. Cevelino, Tyrol.)
Non-graded Sediments. A general term for detrital
sediments, loose or cemented, containing notable
amounts of more than one grade; e.g. , loam,
Non-uniform Pressure. See Directed Pressure.
J. Johnston & P. Niggli : Journ. GeoL, xxi, 1913, p. 599.
J. Johnston : Journ. Geol., xxiii, 1915, p. 732.
Nordmarkite, Brogger, 1890. -- A quartz-bearing
alkali-syenite, the type-rock containing biotite and
segirine as the chief coloured minerals.
W. C. Brogger : Zeif. f. Kryst., xvi (i), 1890, p. 54.
Norite, Esmark. - - A phanerocrystalline rock com-
posed essentially of labradorite and orthorhombic
pyroxene ; if augite be present in addition the
THE NOMENCLATURE OF PETROLOGY 167
rock may be called either hype rite, or hypersthene-
gabbro, according- as hypersthene or augite is the
J. H. L. Vogt : Q.J.G.S., 1909, p. Si.
G. S. Rogers : Ann. New York Acad. Sci., xxi, 1911, p. 29.
A. E. V. Zealley : Trans. Roy. Soc. S. A/., v, 1915, p. i.
Norm, C.I.P.W., 1902. A term applied to the
chemical composition of an igneous rock ex-
pressed in terms of standard " normative "
mineral molecules calculated from the composition
as stated in terms of oxides ; contrasted with the
Mode, which is the actual mineral composition,
C.I.P.W. : The Quantitative Classification of Igneous Rocks,
Normative or Standard Minerals, C.I.P.W., 1902.
A series of ideal mineral-compounds in terms of
which the composition of a rock may be expressed
by a suitable manipulation of the analysis as stated
in oxides, etc. The minerals are divided into salic
and femic groups, and are chosen to afford a simple
standard for comparison, complex minerals such
as the aluminous ferromagnesian minerals being
Northfieldite, Emerson, 1915. An ultra-quartzose
granite containing 83 per cent, of quartz and 13
per cent, of s,oda-orthoclase. (Northfield, Mass.)
B. K. Emerson : Am. Journ. Sci., xl, 1915, p. 215.
Noseanite, Boricky, 1873. A variety of felspathoid
basalt rich in nosean, and free from felspar and
Nosean-phpnoHte, Boricky, 1873. A variety of
phonolite containing nosean (e.g., that of the Wolf
J. J. H. Teall : Brit. Pet., 1888, p. 367.
Novaculite, Cordier, 1868. An aphanitic granulose
or cryptocrystalline rock essentially composed of
quartz, sometimes containing other forms of
1 68 THE NOMENCLATURE OF PETROLOGY
silica, and generally accessory felspar and
garnet ; used as ivhclslone or honestojic.
E. F. Davis : Bull. De-pt. Geol. Univ. California, xi, p. 333,
Obsidian. A volcanic glass, generally black, banded,
or microspherulitic, with a glassy or satiny lustre
and conchoidal fracture.
F. E. Wright : Bull. Geol. Soc. Am., xxvi, 1915, p. 255.
Obsidianite, Walcott, 1898. A term applied to small
balls, buttons, and spheroidal and dumb-bell forms
of dark green to black glass, often pitted and fur-
rowed ; approximating- in composition to obsidian,
but having generally a smaller percentage of
alkalies. Their origin is unknown, but is prob-
ably cosmic, as they occur in Australia and else-
where as discrete bodies often hundreds of miles
from any possible volcanic source. Cf. Australite,
R. H. Walcott : Proc. Roy. Soc. Victoria, xi, 1898, p. 23.
E. J. Dunn : Geol. Surv. Victoria, Bull. 27, 1912.
H. S. Summers : Proc. Roy. Soc. Victoria, xxi, 1909, p. 423;
see also p. 444.
Occult Minerals, Iddings, 1913. A term applied to
minerals which are deduced from chemical con-
siderations to be actually or potentially present
in a hole-crystalline igneous rock, but which for
various reasons cannot be recognised individually.
Thus the detection of K 2 O in a basalt suggests
the presence of orthoclase, which may occur in
crvstals too small for determination, or may be
held in solid solution bv olagioclase.
T. P. Tddings : Igneous Rocks, II, 1013, p. 19.
Ocellar Texture, Posenbusch, 1887. A texture due
to the tangential disposition of minerals such as
biotite, or pyroxene, around the borders of idio-
morphic crystals of later growth, such as analrite
THE NOMENCLATURE OF PETROLOGY 169
Octahedrite. A group name for iron meteorites,
which, on being etched, develop the Widtman-
statten lines, due to the presence of kamasite and
taenite parallel to the octahedral faces.
Odinite, Chelius, 1892. A porphyritic dyke rock of
basaltic composition, containing- phenocrysts of
labradorite andi augite in a groundmass com-
posed of felspar laths and needles of hornblende.
Oikocryst, C.I.P.W., 1906. A matrix or host crystal
through which smaller crystals (chadacrysts) of
other minerals are scattered as poikilitic inclu-
Oil Shale. A fine black or dark-brown shale contain-
ing kerogcn (i.e., material from which crude petro-
leum can be obtained by distillation) and char-
acterised by having a brown streak, a leatherv
appearance with parting-planes often smooth and
polished, and a minutely-laminated structure. It
differs from carbonaceous shale by curling when it
is cut, and by its- toughness and resistance to dis-
integration bv weathering.
Mem. Geol. Surv. Scot. (Oil Shales of the Lothians), 2nd
H. R. J. Conacher : Trans. Geol. Soc. Glasgow, xv, 1917,
Geol. Surv. Spec. Rep. Mineral Resources of Great Britain.
Oje Diabase, Tornebohm. A tvpe of porphyritic
dolerite containing long plagioclase laths in an
aphanitic basaltic groundmass.
Oligodasite, Bombicci, 1868. A variety of granular
olivine-norite which has suffered a certain amount
of alteration. The plagioclase is labradorite in
part, generally saus&uritised, and reduced to
oligoclase with comolementarv secondary products.
Hvpersthene and olivine, with hornblende, chlorite,
and bastite, as alteration products, are the char-
acteristic mafic minerals. By recent authors the
name oligoclasite has been given to phnnrro-
1 7 o THE NOMENCLATURE OF PETROLOGY
crystalline leucocratic rocks composed chiefly of
oligoclase, and it is in this more general sense
that the term is now used.
OligOSite, Turner, 1900. A phanerocrystalline rock
composed almost entirely of oligoclase.
Olivine-. As> a mineral qualifier this name is added to
the names of many igneous rocks, to distinguish
olivine-bearing types from those free from that
mineral, e.g., Olivine -basalt, olivine-theralite, etc.
Olivine-leucitite. = Leudte Basalt.
Olivine-nephelinite. = Nepheline Basalt.
Olivine Rock. = Dunite.
Olivinite, Eichstadt, 1887. A variety of hornblende-
picrite containing augite and anorthite.
Ollenite, Cossa, 1881. A term applied to a variety
of hornblende-schist characterised by abundant
epidote, sphene, and rutile, with smaller amounts
of garnet and other accessories.
(Col d'Ollen, Piedmont.)
Onkilonite, Bacldund, 1915. A variety of felspathoid-
basalt consisting of nepheline, augite, olivine, and
perovskite, with small amounts of leucite and inter-
stitial glass ; felspars and iron-ores are absent.
(Is. of New Siberia.)
H. G. Backlund : Bull. Acad. Sci. St. Peter sbourg, 1915.
Onyx Marble. - - A term applied to compact banded
varieties of calcareous tufa, capable of taking a
G. P. Merrill : Rep. U.S. Nat. Museum, for 1893, p. 593.
Oolite. A rock made up of spheroidal or ellipsoidal
grains formed by the deposition of successive
coats of calcium carbonate around a nucleus.
J. J. H. Teall : Mem. Geol. Surv. (Jurassic Rock? Britain).
Vol. iv, 1894.
F. M. Van Tuyl : Journ. Geol., xxiv, 1016, p. 792.
W. H. Bucher : Journ. Geol., xxvi, 1918, p. 593.
Ooze. A soft incoherent deep-sea deposit composed
almost wholly of the shells and debris of foramim-
fera, diatoms, and other organisms. Cf. Globi-
gerina Ooze, Radiolarian Ooze, etc.
THE NOMENCLATURE OF PETROLOGY 171
Opacite, Vogelsang, 1872. A non-committal descrip-
tive term suggested to avoid periphrasis, for black
opaque grains and scales which may be iron-ores,
or carbonaceous matter, but which are in general
too small for individual determination by optical
For microchemical tests see A. Brammall : Geol. Mag., 1920,
Ophicalcite, Brongniart, 1813. A variety of crystal-
line limestone composed of calcite and serpentine.
Ophite, Palassou, 1819. A general term applied to
the ophitic diabases (dolerites with uralitised py-
roxenes) occurring in the Pyrenees.
A. Lacroix : C.R., clxv, 1917, p. 293.
Ophitic Texture, Michel-Levy, 1877. A texture
characteristic of dolerites, due to the penetration
of pyroxene crystals by laths of plagioclase. A
similar texture is sometimes developed between
other pairs of minerals. When the pyroxene cry
stals wholly enclose a number of plagioclase laths,
the texture becomes a variety of poikilitic texture,
and is distinguished by the term poikilophitic.
A. N. Winchell : Bull. Geol. Soc. Am., xx, 1910, p. 661.
Orbicular Structure, Delesse, 1849. - - A structure
developed in certain phanerocrystalline igneous
rocks (e.g., granites, diorites, and corsite), due
to the occurrence of concentric shells of differ-
ent mineral composition, around centres that may
or may not exhibit a xenolithic nucleus ; = sphe-
roidal, = nodular.
A. C. Lawson : Bull. De-pt. Geol. Univ. California, Pub. 3,
1904, p. 383.
G. A. J. Cole : Sci. Proc. Roy. Dublin Soc., xv, 1916, p. 141.
Orbite, Chelius, 1892. - - A variety of hornblende-
porphyrite containing phenocrysts of hornblende in
a groundmass composed essentially of laths of
plagioclase. (Orbishohe, Odenwald.)
Ordanchite, Lacroix, 1917. - - A variety of hauyne-
tephrite containing phenocrysts of andesine and
orthoclase. (Banne d'Ordanche, Auvergne.)
A. Lacroix : C.R., clxiv, 1917, p. 582.
172 THE NOMENCLATURE OF PETROLOGY
Order, C.I.P.1V., 1902. A division of igneous rocks,
considered after the division into classes, based (in
classes I., II. and III.) on the relative pro-
portions of normative quartz or nepheline to the
sum of the normative felspars. This division
is analogous to the division of rocks into
over saturated, saturated and (as regards fels-
pathoids) under saturated types. In classes IV.
and V. the orders are based on the relative propor-
tions of the normative pyroxenes, and olivine, etc.,
to the sum of the normative iron-ores and titanium
Order of Crystallisation. A phrase loosely employed
for the order in which the minerals of an igneous
rock ceased to crystallise, and determined by such
textural features as the idiomorphism of one mine-
ral to another, and the indentation or enclosure of
one mineral by another. Such features rarely pro-
vide evidence of- the order in which the minerals
began to crystallise.
N. L. Bowen : Jour*. GeoL, xx, 1912, p. 457.
W. Mackie : Trans. Edin. GeoL Soc., ix, 1909, p. 247.
Ore-deposits. A general term applied to rocks con-
taining metalliferous minerals of economic value
in such amount that they can be profitably exploit-
ed. By a double analogy the term is generally
extended to include economically valuable rocks
containing certain non-metalliferous minerals, such
as graphite and diamond ; and also to deposits
which, though they may not be immediately capable
of profitable exploitation, may yet become so by a
change in the economic circumstances that control
Orendite, Cross, 1897. - - A phanerocrystalline rock
composed of leucite and sanidine, with phlogopite
and augite, and therefore a plutonic equivalent of
W. Cross : Am. Journ. Set., iv, 1897, p. 123.
THE NOMENCLATURE OF PETROLOGY 173
OrganogenotlS, Renevier, 1880. A group name
applied to rocks of organic origin.
Ornoite, Cederstrdm, 1893. - - A term applied to a
variety of hornblende-diorite, the chief member of
a suite of rocks in which the felspar varies from
oligoclase to labradorite as the proportion of horn-
blende increases. The rock thus passes into horn-
blende-gabbro, and by decrease of felspar into
hornblende-picrite. (Orno, Sweden.)
Orthoclase-gabbro, Pumpelly, 1880. -- A descriptive
name for rocks now known as monzonite, in which
the plagioclase is at least as calcic as labradorite ;
= Gabbro-syenite. Cf. Granogabbro.
Orthociasite, Merioin, 1915. A medium to fine-
grained dyke-rock containing about 90 per cent, or
more of orthoclase.
U.S.G.S., Prof. Pap. 87, 1915, p. 40.
Orthofelsite, Teall, 1888. A rock containing porphy-
ritic orthoclase in a felsitic groundmass, pheno-
crysts of quartz being absent ; = Orthophyre.
J. J. H. Teall : British Petrography, 1888, p. 291.
Orthogneiss, Roseribusch, 1898. A general term ap-
plied to gneisses derived from rocks of igneous
origin; contrasted with paragneiss (q-v.).
Orthophyre, Coquand, 1851. = Orthoclase Por-
Orthophyric Texture, Rosenbusch, 1896. A ground-
mass texture distinguished from trachytic texture
by the presence of abundant stumpy rectangles of
Orthosite, Turner, 1900. A hololeucocratic phanero-
crystalline rock composed almost entirely of ortho-
Ortlerite, Stache & John, 1879. A variety of horn-
blende-porphyrite containing phenocrysts of horn-
blende in a holocrystalline felspathic groundmass.
(Mte. Confinale, Tyrol.)
i 74 THE NOMENCLATURE OF PETROLOGY
Ossypite, Hitchcock, 1871. A coarse-grained variety
of troctolite composed of labradorite, olivine, and
magnetite, with a little diallage.
(Waterville, New Hampshire.)
Ostraite, Duparc, 1913. A variety of ariegite char-
acterised by abundant magnetite and spinel.
(Ostraia Sopka, Urals.)
L. Duparc : Bull. Soc. franf. Min., xxxvi, 1913, p. i.
Ottajanite, Lacroix, 1917. - - A variety of leucite-te-
phrite richer in plagioclase and poorer in leucite
than vesuvite. Corresponds in chemical composi-
tion to sommaite. (Ottajano, Mte. Somma.)
A. Lacroix : C.R., clxv, 1917, p. 485.
Ottrelite-schist. A schistose rock characterised by
abundant porphyroblastic or embryo-crystals of
ottrelite. (Ottrez, Ardennes.)
Ouachitite, Kemp, 1890. An olivine-free variety
of monchiquite characterised by abundant biotite.
G. H. Williams: GeoL Surv. Arkansas Ann. Re-p., ii, 1890,
Ouenite, Lacroix, 1911. -- A fine-grained eucrite-like
rock containing green augite and anorthite with
smaller quantities of hypersthene and olivine.
Both melanocratic and leucocratic varieties occur.
(Ouen, New Caledonia.)
A. Lacroix: C.R., clii, 1911, p. 816.
Oversaturated, Shand, 1915. -- A term applied to
igneous rocks which contain free silica (quartz,
tridymite, etc.) of magmatic origin.
S. J. Shand : GeoL Mag., 1913, p. 508.
A. Holmes: GeoL Mag., 1917, p. 119.
Oxygen Ratio, Bischof. - - The figure expressing the
following ratio, calculated from the molecular pro-
portions of the constituents of a mineral or rock
Number of atoms of oxygen in the basic oxides.
Number of atoms of oxygen in SiO 2 -
Cf. Coefficient of Acidity.
THE NOMENCLATURE OF PETROLOGY 175
Ozokerite. A compact, waxy, natural hydrocarbon of
various colours, but generally jet-black ; soluble in
turpentine and chloroform = mineral wax = native
Pacific Suite, Harker, 1896. A general term for the
whole assemblage of calc-alkali-rocks, notably re-
presented by andesites, granodiorites, and asso-
ciated rocks ; directing attention to their distribu-
tion around the Pacific, to their association with
Pacific types of coast-line, and more generally to
their association with tectonic structures of the
mountain-building type due to compression, fold-
ing, and overthr ust ing. Cf. Atlantic Suite.
Pahoehoe, Dutton, 1883. An Hawaiian term for fluent
or ropy lava consisting of wrinkled, corded, hum-
mocky flows free from the jagged and scoriaceous
masses characteristic of block-lava ; Dermolithic
lava. Cf. Aa-lava.
Paisanite, Osann, 1893. = riebeckite-micro granite;
riebeckite-quartz-keratophyre ; = ailsyte.
(Paisano Pass, Texas.)
Palagonite, W alter shaus en, 1853. A term applied to
altered basaltic glass, occurring interstitially, as
amygdale fillings, or in tuffs. Palagonite is a
soft, brown or greenish-black cryptocrystalline
substance. (Palagonia, Sicily.)
J. J. H. Teall: Q.J.G.S., liii, i8q 7 , p. 48=;.
Palatinite, Laspeyres, 1869. A term applied to basal-
tic and dioritic rocks containing orthorhombic
A prefix, used particularlv by Continental au-
thors, to indicate the pre-Tertiarv age, and gener-
ally altered character, of the rock to the name of
which is added; e.g. , paltzopicrite. By some
writers the term palceo has been further restricted
T7fi THE NOMENCLATURE OF PETROLOGY
to pre-Carboniferous rocks, those of pre-Tertiary
and post-Devonian age being- indicated by the
prefix 111 c so-.
Paleotypal, Brdgger, 1894. A general term applied to
aphanitic and porphyritic igneous rocks having the
habit or suite of characteristics typical of altered
volcanic and hypabyssal rocks such as many of
those of pre-Tertiary age. By decomposition
felspars have lost their original lustre, and glass,
where present, has become dull through devitrifica-
tion. Rocks having the younger-looking aspect of
fresh volcanic rocks are described as cenotypal
Palimpsest Structure, Sederholm. -- A structure of
metamorphic rocks due to the presence of remnants
of the original texture of the rock.
Palingenesis, Sederholm, 1907. - - The rebirth of a
magma in situ by the fusion of pre-existing rocks
such as granites, gneisses and schists.
J. J. Sederholm : Bull. Comm. G6ol. Finlande, 23, 1907, p.
Pallasite, Rose, 1862. A group name for siderolites,
containing fractured or rounded crystals of olivine
in a network of nickel-iron.
Pan-idiomorphic, Roseribusch. A textural term ap
plied to rocks in which almost all the constituents
Pantellerite, Forster, 1881. - - An alkali-rhyolite or
quartz-soda-trachyte (according to the abundance
of quartz), containing anorthoclase, aegirine and
cossyrite. (Pantelleria, Mediterranean.)
H. S. Washington: Journ. Geol., xxi, 1913, p. 653, p. 683;
xxii, 1914, p. 16.
Paragenesis. -- A term connoting the association of
minerals in characteristic suites considered in rela-
tion to their origin, and implying a deduction of
the processes by which each suite has developed,
or of the order of formation or alteration of
the minerals present in the suite.
THE NOMENCLATURE OF PETROLOGY 177
Paragneiss, Rosenbusch, 1901. -- A term applied to
gneisses formed from detrital sediments such as
arkose ; contrasted with ortho gneiss (q.v.).
Paramagnetism, Faraday, 1845. A property of man}
substances, akin to ferromagnetism, in virtue of
which, when placed in a non-uniform magnetic
field, they tend to move towards the strongest part.
Permanent magnetism is practically absent, and
the susceptibility, which is far smaller than that of
iron, is constant at any given temperature, but is
in most substances nearly inversely proportional to
the absolute temperature. Cf. diamagnetism.
For the application of the magnetic properties of minerals to
their separation see
T. Crook : Science Progress, No. 5, 1907, p. 30.
Paulopost, Evans, 1916. A general term applied to
changes suffered by igneous rocks immediately
after their formation, the changes being a direct
consequence of the consolidation of the magma
(e.g., albitisation, serpentinisation) ; = Penecon-
temporaneous D enteric.
Peach. A local Cornish name for rocks produced by
the alteration of the walls of tin-lodes, and con-
sisting of quartz with chlorite or tourmaline.
Pegmatite, Haiiy, 1822. A term applied to graphic-
granite, and extended to coarse-grained modifica-
tions of granite characterised by irregular segre-
gation of particular minerals rather than by inter-
penetration. The term has also been applied to
other igneous rocks whose names are used as a
prefix, e.g., syenite-pegmatite.
W. O. Crosby & M. L. Fuller : Technology Quarterly, ix,
1896, p. 326.
J. V". Elsden : Geol. Mag., 1904, p. 308.
L. Duparc : Mem. Soc. Phys. et d'Hist. Nat. Geneva, xxxvi,
Pt. 3, 1910, p. 283.
E. S. Bastin : Journ. Geol., xviii, 1910, p. 297.
- U.S.G.S. Bull. 445, 1911.
F. F. Grout : Econ. Geol., xiii, 1918, p. 185.
iy8 THE NOMENCLATURE OF PETROLOGY
Pegmatoid, Evans, 1912. A term suggested to
denote very coarse-grained facies of igneous rock
having a pegmatite-habit, but differing from peg-
matite proper by the absence of graphic texture.
Pelagite. A term applied to the manganese nodules
and concretions of deep-sea deposits ^ Halobolit e.
11 Challenger " Rep. (Deep Sea Deposits), 1891, p. 341.
Pelite, Naumann. - - A general term for clastic sedi-
ments composed of clay, minute particles of
quartz, or rock-flour. A volcanic ash of corres-
ponding grade is called pelitic tuff.
Pencatite. - - A crystalline limestone containing bru-
cite ; calcife and brucite being in approximately
equal molecular proportions (63 per cent, and 37
per cent, respectivelv). Cf. Predazzite.
A. Harker : Mem. Geol. Surv. (Tert. Tg. Rocks, Skye), 1904,
Peperino. A local Italian name for a soft incoherent
yellow-grey tuff, containing broken crystals of fel-
spar, leucite, biotite, and augite, and numerous
rock-fragments embedded in a finely-granular
Per-, C.I.P.W., 1902. A prefix indicating that one
factor is present in extreme amount, its ratio to
another factor being greater than 7/1 ; e.g.,
peralcalic, persalic, etc.
Peridotite, Rosenbusch, 1877. -- A general term for
non-felspathic phanerocrystalline rocks, consisting
of ollvine, with or without other mafic minerals.
Spinellids are the usual accessories.
J. W. Judd : Q.J.G.S., xli, 188=;, p. 354.
A. Harker : Mem. Geol. Surv. (Tert. Tg. Rocks, Skye), 1904,
pp. 63 and 374.
Mem. Geol. Surv. Scot. (Small Isles), 1908, p. 79.
Perknite, Turner, 1901. -- A general term for rocks
composed essentiallv of pyroxenes or amphiboles,
or of members of both groups.
TT. W. Turner : Jonrn. Geol., ix, 1907, p. 507.
THE NOMENCLATURE OF PETROLOGY 170
Perlite. A glassy volcanic rock of rhyolitic compos!
tion with marked perlitic structure.
W. W. Watts : Q.J.G.S., 1, 1894, p. 367.
Perlitic Structure. A structure produced in homo-
geneous material by contraction during- cooling,
and consisting of a system of irregular, convolute,
and spheroidal cracks; generally confined to
natural glass, but sometimes found in quartz, and
other non-cleavable minerals, and as a relict
structure in devitrified rocks.
W. W. Watts : Geol. Mag., 1894, p. 379.
Permanent Set. The permanent change of shape of
a plastic substance due to its imperfection of elas-
ticity, i.e., to the incompleteness of its recovery
after being stressed.
Persilicic, Clarke, 1911. -- A term suggested to re-
place the term acid as applied to igneous rocks ;
for intermediate and basic the corresponding terms
are mediosilicic and subsilicic, respectively.
Petrogenesis. -- A branch of Petrology which deals
with the origins of rocks, and more particularly
with the origins of igneous rocks.
J. P. Tddings : Bull. Phil. Soc. Wash., xii, 1892, p. 89.
C. Doelter : Die Petrogenesis, 1906.
J. P. Id'dings : Prof. Am. Phil. Soc.. 1, 1911, p. 286.
A. Harker : Brit. Ass. Re-p. (1911). 1912, p. 370.
R. A. Daly : Igneous Rocks and their Origin, 1914.
A. Harker : Q.J.G.S., Ixxiii, 1917, p. Ixvii.
A. Holmes: Geol. Mag., 1916, p. 268.
- Q.J.G.S., Ixxii, 1916, p. 271 : and Ixxiv . 1918, pp. 51 and
Petrogratjhical Province, Judd, 1886. A natural re-
gion in which the rocks belonging to a definite
cvcle of igneous activity are characterised bv speci-
fic peculiarities collectively as well as individually,
which distinguish them from other assemblages
of rocks belonging to other regions or cycles.
The possession by the rocks of certain common or
related features as regards chemical and mineral
composition, structure and texture, mode of oc-
180 THE NOMENCLATURE OF PETROLOGY
currence, alterations, associated ore-deposits, and
attendant metamorphic phenomena, is interpreted
to imply community of origin and similarity of
evolution. In any given Petrographical Province
a similar succession of processes, dependent on
the preceding geological history of the region, is
considered to have acted on similar suites of the
raw materials from which the related igneous rocks
were evolved. Thus there is necessarily some
overlapping of adjacent Provinces both in space
and time, and it is rarely that a Province as a
whole can be clearly defined in terms of well-
marked boundaries. = Comagmatic Region.
J. W. Judd : Q.J.G.S., xlii, 1886, p. 54 (Bohemia and Hun-
J. P. Iddings : Bull. Phil. Soc., Wash., p. 128, 1892.
Journ. Geol., i, 1893, p. 166 (Andes).
W. C. Brogger : Eru-ptivgest. Kristiania, i, 1894: ii, 1895;
H. S. Washington : Journ. Geol., vii, 1899, p. 463 (Essex
Bull. Geol. Soc. Am., xi, 1900, p. 389 (Magnet Cove,
T. H. Holland : Mem. Geol. Surv. India, xxviii, Pt. 2, TQOO
A. Lacroix : Nouv. Arch, du Mus. d^Hist. Nat., 4 Ser., i and
v, 1902-3 (Madagascar).
G. T. Prior : Min. Mag., xiii, 1903, p. 233 (Brit. E. Africa
and Atlantic Is.).
F. W. Adams : Journ. Gcol., xi, 1903, p. 239 (Monteregian
A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks, Skye), 1904.
L. V. Pirsson : Am. Journ. Sci., xx, 1905, p. 35 (Montana).
H. S. Washington : Carnegie Inst., Washington, Pub. 57,
1906 (Roman District).
Trans. Am. Inst. Min. Eng., xxxix, 1909, p. 735
A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 88 (General).
N. V. Ussing : Medd. om Grdnland, xxxviii, 1910 (Green-
G. S. Rogers: Ann. New York Acad. Sci., xxi, 1911, p. 11
G. W. Tyrrell : Geol. Mag., 1912, pp. 69 and 120 (late Paleo-
THE NOMENCLATURE OF PETROLOGY 181
H. H. Robinson : U.S.G.S., Prof., Paf. 76, 1913 (San
M. Stark : Fort, der Min. Krist. u. Pet., iv, 1914, p. 251
(General and bibliography).
J. J. O'Neill : Geol. Surv. Canada, Mem. 43 (Pub. No. 1311),
1914 (Monteregian Hills).
W. Cross : U.S.G.S., Prof. Paf., 1915 (Hawaii).
R. A. Daly : Bull. Geol. Soc. Am., xxvii, 1916, p. 325
A. Holmes : Q.J.G.S., Ixxii, 1916-17, p. 260 (E. Africa).
Min. Mag., xviii, 1916, p. 70 (Angola).
A. Harker : In Handbucli der Regionalen Geologic, iii,
i, 1918 (British Isles).
Q.J.G.S., Ixxiii, 1917-18, p. Ixvii (British Is.V
A. Holmes : Min. Mag., xviii, 1918, p. 180 (Arctic Is.).
Petrography. - - A general term for the systematic
description of rocks, based on observations in the
field, on hand-specimens and on thin sections.
Petrography is thus wider in its scope than
Lithology, but more restricted than Petrology,
which implies interpretation as well as description.
In their French usage, however, the terms petro-
graphie and Hthologie are synonymous.
Petrology. A general term for the study by all avail-
able methods of the natural history of rocks, in-
cluding their origins, present conditions, altera-
tions and decay. Petrology comprises petro-
graphy on the one hand, and petrbgenesis on the
other, and properly considered, its subject matter
includes ore-deposits and mineral deposits in gene-
ral as well as " rocks " in the more limited sense
in which that term is generally understood.
Petrosilex. See Felsite.
Phacolith, Harker, 1909. A concordant minor intru-
sion occupying the crest or trough of a fold. Un-
like a laccolith, its form is the consequence of fold-
ing, 'not the cause.
A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 77.
Phanerocrystalline. A term applied to igneous rocks
in which all the crystals of the essential minerals
can be distinguished individually by the naked eye ;
contrasted with aphanitic.
T8 2 THE NOMENCLATURE OF PETROLOGY
Phase, Gibbs. A homogeneous part of any system of
substances which is mechanically separable from
every other homogeneous but dissimilar part of
the system (e.g., a vapour, a solution, or a cry-
stal). Cf. Component.
Phase Rule. A thermodynamic generalisation which
states that in any system
P+f = n+2.
where P denotes the number of co-existing- phases
in the system ;
f denotes the degrees of freedom; and
n denotes the number of independent components
which compose the system.
A. Findlay : The Phase Rule, London, 1918.
PhenocrystS, Iddings, 1892. A general term applied
to the large megascopically visible crystals of por-
L. V. Pirsson : Am. Journ. Set., vii, 1899, p. 271.
T. L. Watson : Journ. Geol., ix, 1901, p. 97.
Phonolite, Klaproth, 1 80 1. An aphanitic rock with
or without phenocrysts), consisting of alkali-fel-
spars and felspathoids, with pyroxenes and amphi-
boles, the mafic minerals being generally soda-
G. T. Prior : Min. Mag., xiii, 1902, p. 237.
Phosphorite. - - A term applied to concretionarv
masses or metasomatised rocks, consisting- mainly
of calcium phosphate (hydro- or fluo-calcium car-
O. Stutzer : Zeit. f. Prakt. GeoL, xix, 1911, p. 73.
A. L. du Toit : Geol. Surv. S. Af. Mem., 10, 1917.
PhreatlC, Daubree, 1887. A term applied to ground-
waters, i.e., to seepage waters occurring at and
below the water-table, drainage waters above the
water-table being- called vadose.
R. A. Daly : Econ. Geol., xii, 1917, p. 494.
Phtanite, Haily. A term applied to compact crypto-
crystalline silicified shales and other siliceous rocks
such as lydite, hornstone, etc. =Phthanitc.
G. F. flecker: U.S.G.S., Mon. xiii, 1888, p. 105.
THE NOMENCLATURE OF PETROLOGY 183
Phyllite, Naumann. - - A compact lustrous schistose
rock with its minerals less well defined than in a
mica-schist, the characteristic mineral by which
the foliation is controlled being sericite.
Picrite, Tschermak, 1866. A melanocratic rock which
differs from peridotite in containing a small amount
of felspar (usually labradorite). The term has also
been extended to include similar rocks, often asso-
ciated with teschenites, in which analcite is pre-
sent. These should be distinguished as Analcite-
G. W. Tyrrell: Q.J.G.S., Ixxii, 1916-17, p. 84.
A. Holmes : Geol. Mag., 1917, p. 150.
Picrite-basalt. A melanocratic basalt characterised
by abundant micro-phenocrysts of olivine and au-
gite, in a groundmass containing only a small pro-
portion of labradorite ; = Felspathic limburgite.
A. Holmes : Q.J.G.S., Ixxii, 1916-17, p. 244.
Pieiiaarite, Brouwer, 1910. A melanocratic variety
of aegirine-foyaite characterised by exceptional
richness in sphene. (Bushveld.)
Piezocrystallisation, Weinschenk, 1900. A term ap-
plied to the crystallisation of a viscous and con-
strained magma during the operation of powerful
directed pressure, the latter condition implying
that the normally-formed pyrogenetic minerals
may not be stable as they would be under condi-
tions of hydrostatic pressure.
E. Wienschenk : Cong. Geol. Inter., C.R., \iii (1900), p. 326.
Pilandite, Henderson, 1898. A variety of porphyry
characterised by the abundance of anorthoclase as
phenocrysts and in the groundmass; the porphy-
ritic equivalent of hatherlite.
Pillow Lavas, Bonney, 1893. A general term applied
to basaltic or albitised basaltic rocks that exhibit
ellipsoidal or pillow structure.
H. Dewey & J. S. Flett : Geol. Mag., 1911, p. 202, p. 241.
J. V. Lewis : Bull. Geol. Soc. Am., xxv, 1914, p. 595.
i4 THE NOMENCLATURE OF PETROLOGY
Pilotaxitic Texture, Rosenbusch, 1887. A texture,
developed typically in the groundmass of certain
undesites, due to a felt-like interweaving of felspar
microlites ; probably a variety of micropoikilitic
texture in which the host mineral is generally
PhlOlite, Rumpf, 1873. A metamorphic rock contain-
ing crystals and granular aggregates of magnesite
(breunnerite variety) in a schistose matrix which
may be phyllite or talc-schist. The rock derives
its name from the resemblance of the magnesite
bodies to pine cones. (Styria.)
T. Crook : Trans, Ceramic Soc., 1919^ P- 81.
Pipe-amygdales, Cohen, 1875. ~- Amygdales of pipe-
like form extending upwards with swellings or
bifurcations from the base of a lava-flow 7 , to which
they may be normal or inclined. The form and
location of these amygdales are probably due to the
flow of lava over a moist floor.
A. L. Du Toit : Geol. Mag., 1907, p. 13.
Piperno. A local Italian name given to the trachytic
tuffs or eutaxitic trachytes of the Phlegrean Fields.
Pisolite. A coarse-grained variety of oolite made up
of oolite-grains of about the size of a pea.
Pitchstone. A term applied to more or less devitrified
glassy igneous rocks of various compositions,
characterised externally by a dull pitch-like lustre,
and internally by the presence of crystallites.
Rhyolite-, dacite-, andesite-, and other varieties of
pitchstone are distinguished when evidence of
composition is available.
A. Scott : Trans. Geol. Soc. Glasgow, xv, 1914, p. i.
E. M. Anderson & E. G. Radley : Q.J.G.S., Ixxi, 1915, p.
Plagiaplite, Duparc & Pearce, 1902. - - A dioritic
aplite containing oligoclase or andesine with sub-
ordinate amounts of hornblende and micas. By
the incoming of quartz the type passes into glad-
kaite. ' (Koswa, N. Urals.)
L. Duparc & P. Pamfil : Bull. Soc. franf Min., xxxiii, 1910,
THE NOMENCLATURE OF PETROLOGY 185
Plagiophyre, Tyrrell, 1912. -- A term for rocks
resembling orthophyres in texture, but containing
plagioclase instead of orthoclase. The type
example contains laths of andesine with interstitial
chloritic minerals, iron-ores, and, in places, ortho-
clase. Cf. Leucophyre.
(Carrick Hills, Ayrshire.)
G. W. Tyrrell : Trans. Geol. Soc. Glasgow } xv, 1912-13, p. 77.
Planophyric, C.I.P.W., 1906. A term applied to por-
phyritic rocks in which the phenocrysts are ar-
ranged in layers.
Plasticity. The property of a substance whereby it
can be permanently deformed without rupture. A
plastic solid is one in which recovery from a state
of strain is only partial. The permanent deforma-
tion thus produced is called permanent set. The
stress just necessary to cause permanent set is
called the elastic limit, and a body strained beyond
this limit flows until the stresses are reduced be-
low it. When the elastic limit is zero, as in
pitch, and permanent set is acquired at a rate pro-
portional to the shearing-stress applied, the plas-
ticity (viscosity of some authors) is described as
L. Milch : Geol. Rund., ii, 1911, p. 145.
F. D. Adams & J. A. Bancroft : Journ. Geol., xxv, 1917,
H. Jeffreys : See Geol. Mag., 1916, p. 126.
Platy Structure. A structure due to differential con-
traction during cooling, occurring in lavas and in-
trusions as a series of fractures parallel to the
cooling surface. Igneous rocks may thus be
cracked into thin plates or tabular sheets, which
give them a stratified appearance, especially as
seen in the field when the structure has been
developed by weathering.
Plauenite, Brogger, 1895. The type syenite of
Plauen, near Dresden.
H. S. Washington : Am. Journ. Sd., xxii, 1906, p. 132.
i86 THE NOMENCLATURE OF PETROLOGY
Pleochl'OlC Haloes. A term applied to coloured zones
occurring around radioactive inclusions (e.g., zir-
con) in certain minerals (e.g., micas, tourmaline,
cordierite), characterised by darker tints than the
enclosing mineral, by pleochroism, and by a zoned
structure. The zones are parallel to the periphery
of the inclusion, about which they have developed
as a consequence of the emission of a - particles
(helium atoms, positively charged) from the radio-
active elements contained in it. = Radio-haloes.
J. Joly : Phil. Mag., xix, 1910, pp. 321 & 630; xxv, 1913,
Phil. Trans. Roy. Soc., ccxviiA, 1917, p. 51.
Plumasite, Lawson, 1903. A phanerocrystalline rock
consisting essentially of oligoclase and corundum.
(Plumas Co., California.)
A. C. Lawson : Bull. De-pt. Geol. Univ. California, iii, 1903,
"Plus" Minerals, Lcewinson-Lessing, 1897. A term
applied to minerals (such as felspars) whose mole-
cular volumes are greater than the sum of the
molecular volumes of the constituent oxides. In
the case of allotropic modifications of the latter,
that having the larger molecular volume is used in
the calculation. Cf. " Minus " Minerals.
F. Lcewinson-Lessing : Cong. Geol. Inter., C.R., vii, 1897,
Plutonic- A general term applied to major intrusions
and to the rocks of which they are composed, sug-
gestive of the depths at which they were formed
in contradistinction to most minor intrusions and
all volcanic rocks.
Pneumatolysis, Buns en. The process whereby mine-
rals (whether occurring in ore-deposits or not) are
produced wholly or in part from volatile com-
pounds of one or other of their constituents, the
agents concerned being the magmatic gases known
as miner alisers.
A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 282.
Poecilitic Texture. See Poikilitic.
THE NOMENCLATURE OF PETROLOGY 187
Poikilitic Texture, Williams, 1886. - - A texture in
which small granular crystals are irregularly scat-
tered without common orientation in larger crys-
tals of another mineral. The term has also been
applied to the variegated marls of the Trias.
G. H. Williams : Journ. Geol., i, 1893, p. 176.
Poikiloblastic. Becke, 1903. A metamorphic texture
due to the development, during recrystallisation, of
a new mineral around numerous relics of the
original minerals, thus simulating the poikilitic
texture of igneous rocks. When the included
relics also reveal the original texture of the rock,
the new texture is helicitic (<J.^-)-
PoikiloohitlC Texture, Johannsen, 1911. - - A term
suggested for a varietv of ophitic texture in
which the pvroxenic matrix completelv includes
laths of plagioclase, and is not merely penetrated
Pollenite. Lacroix, IQO7. A heteromorphic variety of
campanite containing orthoclase. subordinate
olioDclase, sodalite, and nepheline, with biotite,
olivine, melanite, and sphene.
(Pollen a, Mte. Somma.)
A. Lacroix : Nouv. Arch, du Mus. (THist. Nat., ix, 1907,
Polzenite, Scheumann, 1913. A variety of melilite-
basalt. (Polzen, Bohemia.)
Ponzite, Washington, 1913. A term suggested for
trachytes of the Ponza type (Rosenbusch) ; charac-
terised by the presence of pyroxene (diopside and
Eegirine-augite) as the chief mafic mineral.
Porcellanite. A compact thermallv-metamorphosed
rock of light colour and porcelain-like appearance,
derived from marls or shales.
Porfido rosso antico. The withamite-bearing horn-
blende-porphyrite of Djebel Dokhan in Egypt.
Porosity. The ratio, P, expressed as a percentage, of
the volume, V p , of the pore-space in a rock to the
1 88 THE NOMENCLATURE OF PETROLOGY
volume, V r , of the rock, the latter volume includ-
ing- rock material plus the pore-space.
P == 100 V p /V r .
J. Allen Howe : The Geology of Building Stones, London,
iQ'o, p. 313-
A. L. Du Toit : Trans. Roy. Soc., S. Africa, iv, 1915, p.
A. Holmes : The Geological and Physical Characters of
Concrete Aggregates, B.F.P.C. Red Book. 256, 1920, p.
133. Petro graphic Methods and Calculations, 1920.
Porphyrite. A term which has been variously used
for pre-Tertiary andesitic rocks, altered andesite
rocks, and hypabyssal rocks of marked porphyri-
tic texture and andesitic composition. The last
usage referred to is that now customary. The
phenocrvsts are generally plagioclase (average
composition that of andesine) and mafic minerals,
and the groundmass is holocrvstalline and more
coarsely grained than in andesite. To avoid con-
fusion some writers prefer terms such as diorite-
porphyry and andesite-porphyry. Cf. Porphyrv.
Porphyritic Texture. A texture of igneous rocks due
to the presence of crystals (phenocrvsts) which are
conspicuously larger than the mineral individuals
of the groundmass through which they are sprin-
Porphyroblast, Becke, 1900. - - A term given to the
pseudo-porphyritic crystals of rocks produced by
thermodynamic metamorphism. The correspond-
ing texture is called porphyroblastic.
Porphyroclastic Structure, Becke, 1903. - - See
Mortar or Murbruk Structure.
Porphyro-granulitic Texture, Judd, 1885. A texture
of certain dolerites which contain phenocrysts of
felspar and olivine in a base of lath-shaped fel-
' spars and irregular grains of augite ; i.e., a com-
bination of porphyritic and intergranular textures.
J. W. Judd : QJ.G.S', xli. 1885, p. 761.
Porphyroid, Los sen, 1869. -- A term applied to
porphyroblastic metamorphic rocks intermediate
THE NOMENCLATURE OE PETROLOGY 189
structurally between hallefiinta and granite-gneiss,
in the same way as quartz-porphyry or granite-
porphyry are intermediate between rhyolite and
granite. The term has been extended to include
porphyroblastic schists of sedimentary origin.
P. Quensel : Bull. Geol. Inst. U-psala, xii, 1913, p. 265.
Porphyry. A term first given to an altered variety of
porphyrite (porphyrites lapis) on account of its
purple colour, and afterwards extended by com-
mon association to all rocks containing conspicu-
ous phenocrysts in a fine-grained or aphanitic
groundmass. The resulting texture is described
as porplivritic. In its restricted usage, without
qualification, the term porphyry usually implies a
hypabyssal rock containing 1 phenocrysts of alkali-
felspar, though in the field it is generally allowed
a wider scope, and commercially it is used for all
porphyritic rocks. With mineral- and rock-name
qualifiers it is used in combinations such as quartz-
porphvrv, nepheline-porph\iry, granite-porphyry,
etc., while in an amputated form, -phyre, first intro-
duced by Brongniart in 1813, and used as a suffix,
it appears in terms such as mclaphyre, lampro-
phyre, leucitophyre, etc.
Prasinite, Kalkowsky, 1886. A variety of green
schist, in which hornblende, chlorite, and epidote
are present in approximately equal proportions.
Predazzite, Petzlioldt. - - A variety of dedolomitised
crystalline limestone containing- brucite, the latter
mineral being in less amount than in pencatite, in
which the molecular proportions of CaO : MgO
are those of dolomite. (Predazzo, Tyrol.)
A. F. Rogers : Aw. Joitrn. Sci., xlvi, 1918, p. 582.
Primary Igneous Gneiss, Harker. See Gneissose
Propylite, v. Richthofen, 1868. - - A name given to
hydrothermally-altered varieties of andesite or
dacite ; generally containing secondary calcite and
silica, chlorite and sulphides.
J. W. Judd : Q.J.G.S., xlvi, 1890, p. 341.
i 9 o THE NOMENCLATURE OF PETROLOGY
Propylitisation. - The late-mag-matir processes, in-
volving- the introduction of carbon-dioxide,
sulphur, and water, whereby andesitic and related
rocks are altered.
Proteolite, Boase, 1832. An old term for hornfelsic
rocks. Bonney proposes to revive the term for
hornfels composed of quartz, mica, and andalusite.
T. G. Bonney : Q.J.G.S., xlii, 1886. p. 104.
Proterobase, Gunibel, 1874. An altered doleritic or
basaltic rock containing- purple-brown aug-ite and
primary brown hornblende, and characterised bv
the presence of secondary green hornblende and
other alteration products. The rock to which the
name was first applied is a Silurian diabase in the
J. S. Flett : Mem. Geol. Surv., 335-336 (Padstow and Camel-
ford), IQIO, p. 43.
Protoclastic Structure. A structure produced by the
granulation of minerals of early formation, the
granulation being- due to differential flow of the
partlv consolidated mag-ma from which the frac-
tured minerals separated.
Protogenqus, Naumann, 1858. -- A group name for
" original " rocks as opposed to "derived" rocks,
and including- saline deposits, coal, igneous rocks,
and ore-deposits. The term is no longer used.
Cf. D cut erogenous.
Protogine, ]urine, 1806. A term applied to the cen-
tral granite of the Alps, which, being gneissose in
structure, and containing sericite, chlorite, epidote
and garnet, is considered to be of composite ori-
gin or else to have crystallised, or in part to have
recrvstallised, under stress during or after con-
L. Duparc et L. Mrazec : Arch. Sci. Ph-ys. et Nat., Geneva,
Protomylonite, Backlund, 1918. - - A mylonitic rock
produced from contact-metamorphic rocks, granu-
lation and flowage being due to overthrusts
THE NOMENCLATURE OF PETROLOGY 191
following, in the first place, the contact-surfaces
between the intrusion and the country-rock. The
first rocks to be crushed and rolled out during- the
process are thus the metamorphic rocks already
produced in contact with the intrusion.
II. G. Backlund : Geol. For. Fork., xl, 1918, p. 195.
Prowersite, RosenbuscK^ 1908, after Prowersose,
Cross, 1906. A syenitic lamprophyre of fine grain,
containing- abundant biotite and orthoclase, with
smaller amounts of augitej^ altered olivine, and
iron-ore minerals. A variety containing porphy-
ritic perthite is also known.
(Prowers Co., Colorado.)
W. Cross : ] ourn. Geol., xiv, 1906, p. 165 ; see also p. 173.
Psephicity, Mackie, 1897. - - The degree of " round-
ness " characterising pebbles or sand-grains. The
coefficient of psepliicity is the ratio of specific
gravity to hardness, and roughly expresses the
relative facility with which minerals can be
W. Mackie : Trans. Edin. Geol. Soc., vii, 1897, p. 301.
Pseudo-Conglomerate. An autoclastic conglomerate
formed by fragmentation and rolling nearly in situ,
due to the action of orogenic forces ; = Crush-con-
Pseudo-porphyritic. A metamorphic texture due to
the development during recrystallisation of large
well-defined crystals, such as those of garnet in
mica- and chlorite-schists ; = Porphyroblastic.
Psettdotachylyte, Shand, 1914. A black rock exter-
nally resembling tachylyte and occurring in irre-
gularly branching veins. The material carries
fragmental enclosures, and shows evidence of
having been at a high temperature ; microlitic and
spherulitic crystallisation took place in the ex-
tremely dense base. Pseudotachylyte differs from
flinty crush-rock (q.v.) in its intrusive habit, and
in the absence of any structures referable to local
crushing. (Parijs, Orange Free State.)
S. J. Shand : Q./.G.S., Ixxii, 1916-17, p. 198.
192 THE NOMENCLATURE OF PETROLOGY
PteifOpod Ooze, Murray, 1873. A calcareous deep-
sea deposit characterised by an abundance of
J. Murray & A. F. Renard : " Challenger'- Ref. (Deep Sea
Deposits), 1891, p. 223.
Ptygmatic Folding, ScJerholm, 1907. -- A term pro-
posed for the primary folding in migmatites (injec-
tion gneisses, etc.), caused by the processes to
which the migmatites owe their origin and com-
J. J. Sederholm : Bull. Co/urn. Geol. Fiulande, No. 23. 1907,
Puddingstone. -- A popular term for conglomerates,
consisting of well-rounded pebbles set in an abun-
dant matrix. The Hertfordshire Puddingstone, to
which the name is most commonly applied, is a
local facies of the Reading- Pebble-beds, which has
been cemented into a hard siliceous flint-con-
G. Barrow : Proc. Geol. Assoc., xxx, 1919, p. 5.
Puglianite, Lacroix, 1917. A phanerocrystalline rock
composed essentially of augite, leucite, and anor-
thite. (Mte. Somma.)
A. Lacroix : C.R., clxv, 1917, p. 210.
Pulaskite, Williams, 1890. A porphyritic nepheline-
syenite containing soda-orthoclase, with aegirine-
augite, barkevikite, and biotite as its characteris-
tic mafic minerals/ (Pulaski Co., Arkansas.)
Pumice. A general term applied to lavas so extreme'}
vesiculated as to resemble froth. Varieties of
rhyolitic composition are generally light-coloured
and characterised by a sub-pearly lustre.
PumiceOUS Structure. A structure akin to that of a
coarse froth, due to the extreme vest culat ion of a
lava by expanding gases and vapours.
Pyribole, Joliannsen, 1911. A general term for mine-
rals belonging to either the pyroxene or arnphibolc
groups, suggested for field use.
THE NOMENCLATURE OF PETROLOGY 193
PyroclastS. A general term for fragmental deposits
of volcanic ejectamenta, including volcanic con-
glomerates, agglomerates, tuffs, and ashes.
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191.
J. F. N. Green : Proc. Geol. Assoc., xxx, 1919, p. 153.
Pyrogenetic Minerals. A term applied to the primary
magmatic minerals of igneous rocks, excluding
those due to pneumatolytic, hydrothermal, and
thermodynamic processes. In practice many cases
of doubtful character arise, since the solidification
of a magma may constitute 'a continuous process
beginning with indubitable pyrogenetic minerals,
and yet finishing with a well-defined hydrothermal
series of minerals.
Pyromeride, Montetro, 1814. A quartz-felsite or
devitrified rhyolite characterised by conspicuous
spherulitic or lithophysal structure, and thus hav-
ing a nodular appearance.
J. Parkinson : Q.J.G.S., liv, 1898, p. ioi.
Pyroxenite, Coquand, 1857. - - A general term for
phanerocrystalline rocks consisting predominantly
of pyroxenes. Both quartz- and olivine-bearing
varieties are recognised, and those containing
segirine-augite or traces of felspathoid are referred
to as alkali-pyroxenite. Although the above usage
is now customary in English-speaking countries, it
should be noticed that in France the term pyro-
xenite is given to melanocratic facies of pyroxene
Pyroxenolite, Lacroix, 1894. - - A general term for
phanerocrystalline rocks of igneous origin, consist-
ing predominantly of pyroxenes ; pyroxenite
(French usage) being restricted to metamorphic
rocks of the same mineral composition.
i 9 4 THE NOMENCLATURE OF PETROLOGY
Quartz-barytes Rock, Holland, 1897. A rock com-
posed of about 30 per cent, barytes and 70 per
cent, quartz, and considered to be of magmatic ori-
gin, occurring in the Salem district of Madras as
a network of pegmatite-like veins.
T. H. Holland : Rec. Geol. Surv. India, xxx, 1897, p. 236.
Quartz-dlorite. -- A phanerocrystalline igneous rock
composed of quartz, plagioclase (averaging oligo-
clase or andesine), hornblende, and generally
biotite. If orthoclase be present in addition, but
in amount inferior to that of the plagioclase, the
rock is then described as granodiorite. Cf.
Quartz-dolerite. An oversaturated variety of dolerite
containing interstitial quartz. The latter mineral
is frequently associated with orthoclase in micro-
pegmatite, and when this is present the rock is
described as grano dolerite.
Mem. Geol. Surv. (Glasgow District), 1911, pp. 118 and 146.
G. W. Tyrrell : Geol. Mag. 1909, p. 299.
Quartz-felsitC. A rhyolite or quartz-porphyry having
a cryptocrystalline or devitrified groundmass ; in
the older usage of the name it was synonymous
with quartz-porphyry, but the latter term is now
more commonly used, especially when conspicuous
phenocrysts are present.
Quartzite. A granulose metamorphic rock, represent-
ing a recrystallised sandstone, consisting pre-
dominantly of quartz. The name is also used for
sandstones and grits cemented by silica which
has grown in optical continuity around each frag-
W. J. Sollas : Set. Proc. Roy. Dublin Soc., vii, 1892, p. 169.
L. Cayeux : Structure et Origine des Gres du Tertiare
farisien, Paris, 1907.
Quartz-porphyry. A rock containing phenocrysts of
quartz and alkali-felspar, typically orthoclase, with
or without mica, in a cryptocrystalline or micro-
THE NOMENCLATURE OF PETROLOGY 195
crystalline groundmass. If phenocrysts are abun-
dant the rock becomes granite-porphyry, while if
they are absent or inconspicuous, the terms quartz-
felsite and microgranite are used according to the
nature of the groundmass.
J. Morrison : Q.J.G.S., Ixxiv, 1918-19, p. 116.
Quartz-schist. A schist in which the foliation is due
to the presence of streaks and lenticles of non-
granular quartz. Mica is usually present, but in
less amount than in mica-schist.
Queluzite, Derby, 1901. A manganese-garnet (spes-
sartite) rock, in some varieties containing amphi-
boles, pyroxenes or micas, with or without free
manganese-oxides. Residual deposits derived
from this rock constitute valuable manganese-ores.
(Queluz, Minas Geraes, Brazil.)
O. A. Derby: Am. Journ. Sci., xii, 1901, p. 18; xxv, 1908.
Radio-activity. --An atomic property of certain ele-
ments belonging to the uranium and thorium
families, whereby they spontaneously disintegrate
with external emission of energy, carried in the form
of a- particles (positively charged helium atoms) or
^-particles (electrons), into elements of lower in-
trinsic energy, and, where a-particles are lost, of
lower atomic weight. Owing to the distribution of
radioactive elements in the earth's crust, radio-
thermal phenomena are of critical importance in
air geological processes in which heat is an active
A. Holmes : Science Progress, No. 33, 1914, p. 12.
Geol. Mag,, 1915, pp. 60, 102 ; 1916, p. 265.
Proc. Geol. Assoc., xxvi, 1915, p. 289.
Q.J.G.S., Ixxiv, 1918-19, pp. 63, 84.
Radio-haloes, Hirschi, 1920. See Pleochroic Haloes.
196 THK NOMENCLATURE OF PETROLOGY
Radiolarian Ooze, Munay, 1873. A variety of red
clay (q.v.) characterised by an abundance of the
siliceous skeletons of radiolaria and of certain
J. Murray & A. F. Kenard : " Challenger" Rep. (Deep Sea
Deposits), 1891, p. 203.
Raglanite, Adams -> Barlow, 1910. A facies of
nepheline-syenite containing in order of abundance,
oligoclase, nepheline, and corundum, with small
quantities of micas, calcite, magnetite, and apatite.
F. D. Adams & A. E. Barlow : GeoL Surv. Canada Mem. 6
(Pub. No. 1082), 1910, p. 314.
Randannite, Salvetat. A local variety of diatomace-
ous earth occurring in the neighbourhood of the
Rang, C.I.P.W., 1902. A division of igneous rocks
considered after the division into orders, based (in
classes I., II. and III.) on the relative proportions
of the molecules of salic K 2 O and Na 2 O to those
of salic CaO. This division is analogous to the
more general division of rocks into alkali- and cdlc-
alkali types, and usually fails to express the kind
of felspar present. In classes IV. and V. the
rangs are based on the relative proportions of the
molecules of MgO,FeO, and femic CaO to those
of femic K 2 O and Na. 2 O. This is analogous to the
division of perknites, peridotites and similar rocks
into normal and alkali-types.
Rapakivi, Sederholm, 1891. A hornblende-biotite
granite containing large rounded crystals of ortho-
clase mantled with oligoclase. The same term
has also been applied to the youngest pre-Cam-
brian granites of the Christiania District.
Ratio of Absorption. The ratio, A, expressed as a
percentage of the volume V p of the pore-space in
a rock to the weight W of the rock when dry.
A = 100 V P /W.
A. Holmes : 7 'he Geological and Physical Characters of
Concrete Aggregates, B.F.P.C. Red Book, 256, 1920, p.
THE NOMENCLATURE OF PETROLOGY 197
Reaction Rim. A term applied to a peripheral zone
of mineral aggregates formed around one mineral
(e.g., hypersthene), by reaction with another (e.g.,
plagioclase), with which it would otherwise come
into contact. Cf. Kelyphitic; Corona.
T. H. Holland : Mem. Geol. Surv. India, xxix, 1896, p. 20.
Red Clay. A widespread deep-sea deposit consisting
of ferruginous clayey alteration products of vol-
canic debris, wind-borne particles from desert
regions, zeolite crystals, concretionary manganese
and iron oxides, meteoritic matter, and a variable
content of siliceous or calcareous remains. Where
the depth is great organic remains may be entirely
absent owing to the solvent action of sea-water
which overtakes them as they sink towards the
ocean floor. At suitable depths and beneath a
suitable environment the red clay passes laterally
into globigerina ooze, radiolarian ooze, or diatom
ooze, all of which have an inorganic residue
resembling red clay.
J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea
Deposits), 1891, p. 190.
Red Mud.- A reddish-brown terrigenous deep-sea mud
which accumulates on the sea-floor in the neigh-
bourhood of deserts and off the mouths of great
rivers ; contains CaCO 3 up to 25 per cent.
J. Murray : " Challenger " Re-p, (Deep Sea Deposits), 1891,
Refractories or Refractory Materials. - - Materials
which will withstand with at least some degree of
success the effects of the heat and chemical re-
actions involved in metallurgical and other high-
temperature processes. They are classified as
Acid e.g., fireclay, ganister, and sand;
Neutral e.g., chromite and graphite; and
Basic e.g., bauxite and magnesite.
R. Iladneld : Trans. Faraday Soc., xi, 1916.
P. ('. H. Boswell : British Resources of Refractory Sands,
Pt. i, 1918.
Mem. Geol. Surv., Spec. Rep. Min. Resources, vi, 1918.
T. Crook : Trans. Ceramic Soc., 1919, p. 67.
1 98 THE NOMENCLATURE OF PETROLOGY
Regional Metamorphism, Daubree, 1860. A general
term for metamorphism due to the sum of the pro-
cesses which have affected the rocks over exten-
sive areas ; contrasted with local metamorphism in
which each area affected is restricted to an aureole
of limited extent, and related to a definite
intrusion of magma. Originally the term covered
changes due to deep burial and the action of heat
and hot gases from the interior ; by many writers
it has been used as synonymous with dynamic
metamorphism, and by others in the sense defined
above, but with the proviso that the metamorphism
is not genetically connected with the intrusion of
magmas. This specified limitation would often
be difficult to substantiate, for many of the fea-
tures of regional metamorphism are not distin-
guishable from those of local or contact metamor-
phism, except in uniformity, depth and extent.
F. D. Adams : Q.J.G.S., Ixiv, 1908, p. 127.
G. Barrow : Proc. Geol. Assoc., xxiii, 1912, p. 274.
R. A. Daly : Bull. Geol. Soc. Am., xxviii, 1917, p. 394.
For other references see under Metamorphism.
Regolith, Merrill 9 1906. A general term for the super-
ficial blanket of denudation products which is
widely distributed over the more mature f< solid "
rocks. The term includes weathering residues,
alluvium, and aeolian and glacial deposits.
G. P. Merrill : Rocks, Rock Weathering, and Soils, 1906,
Resorption. - - The partial or complete solution by a
magma of a mineral, or its components, with
which it is not in equilibrium, or with which,
owing to changes of temperature, pressure, or
composition, it has ceased to be in equilibrium,
The term is often wrongly applied to immature
crystals, and to crystals which have decomposition
borders through change of pressure or otherwise.
O. Andersen : Am. Journ. Sci., xxxix, 1915, p. 451.
THE NOMENCLATURE OF PETROLOGY 199
Resurgent, Daly, 1908. A term applied to magmatic
emanations derived not from the magma itself
(juvenile), but from entrapped country rock.
R. A. Daly : Econ. Geol., xii, 1917, p. 491.
Rhomb-porphvry, or Rhombenporphyr, v. Buch.A
variety of alkali - syenite - porphyry containing-
phenocrysts of anorthoclase or potash-oligoclase
(rhomb-shaped in section), small augites and occa-
sionally olivine, in a fine-drained groundmass con-
sisting- mainly of alknli-felspars ; Kenyte (in
P. Quensel : Bull. Geol. 7ns/. U-psala, xvi, 1918, p. i.
Rhyobasalt. Shand, 1017. - - A term suggested for
rocks which are the effusive equivalent of grano-
Rhyocrvstal, Wright, 1902. A term applied to
crystals of idiomorphic outline which are arranged
A. C. Lane : Bull. Geol. Soc. Am., xiv, 1002, p. ?86.
Rhyolite, v. Richthofen, 1861. A volcanic rock cor-
responding in chemical composition to granite,
and generally having small phenocrysts of quartz
and othoclase (or other alkali-felspar) in a glassy
or cryptocrystalline groundmass. Flow structure
is commonly developed, and spherulitic, nodular,
and lithophysal structures are exhibited by many
J. P. Tddings : U.S.G.S., jth Ann. Re<p. (1885-6), 1888, p. 255
A. Harker : Bala Volcanic Series, 1889, p. 9 (N. Wales).
H. Backstrom : Geol. For en i Stockholm Fork, xiii, 1891,
p. 637 (Iceland).
G. A. J. Cole : Sci. Trans. Roy. Dublin Soc., vi, 1896, p.
J. P. Iddings : U.S.G.S., Mon. xxxii (ii), 1899, p. 356
W. S. Boulton : Q.J.G.S., Ix, 1904, p. 450 (Pontesford Hill).
H. H. Robinson : U.S.G.S., Prof. Pa-p., 76, 1913, p. 103
Riecke's Principle. A thermodynamic principle which
states that, since the vapour pressure of a sub-
200 THE NOMENCLATURE OF PETROLOGY
stance is increased by external pressure, solution
(e.g., of a mineral) tends to take place most readily
at points where the pressure is greatest, and re-
crystallisation where the pressure is least.
Rigidity. - - The property possessed by solid bodies
whereby they offer an elastic resistance to deforma-
tion. See Elasticity of Form.
Rigid Solution, Iddings, 1913. -- A term applied to
rock-gflass to connote its physical state, in contra-
distinction to a solid solution which implies a
Ring-dyke. A dyke which follows the course of an
irregular ring-like fault, and of which the outcrops
approximate to a closed curve more or less broken
according to the conditions favouring exposure.
Geol. Surv. Summ. Prog. (1914), 191^, p. 36.
E. B. Bailey : Geol. Mag., 1919, p. 466.
Ripple-mark. An undulating- surface-form produced
by waves or currents of air or water at their con-
tacts with unconsolidated sediments, the surface
being thrown into a series of alternating ridges
and furrows, which trend at right-angles or
obliquely to the direction of the flow of the moving-
fluid, and which, hvdrodynamically, represent sur-
faces of minimum friction.
E. M. Kindle : Geol. Surv. Canada, Museum Bull., 25, 1917.
W. H. Bucher : Am. Journ. Sci., xlvii, 1919, pp. 149 and 241.
Ripple-mark Index, Kindle, 1917. The ratio of wave-
length (horizontal distance from crest to crest, or
from trough to trough) to twice the amplitude (ver-
tical distance from trough to crest). For ripple
marks due to water currents the ratio varies from
20 to 30, whereas for those due to air currents
(wind) the ratio varies from 3 to 6. The index,
therefore, provides a criterion of the origin of the
E. M. Kindle : Gee.. Surv. Canada, Museum BnU,, 2$, 1917,
THE NOMENCLATURE OF PETROLOGY 201
RlZZOnite, Doelter, 1903. A term applied to a local
variety of limburgitc. (Mt. Rizzoni, Tyrol.)
C. Doelter : Am. Akad. Wisch. Wien, xl, 1903, p. 10.
Rock. As a geological concept, rock may be defined
as (a) any formation of natural origin that con-
stitutes an integral part of the lithosphere, and that
cannot be referred to a single fossil, or to a single
individual of a mineral species ; or (b) a representa-
tive specimen of such a formation.
" It is as the architectural elements of the earth's
crust, rather than as aggregates of minerals or
chemical constituents, that rocks are best and most
fundamentally considered ; and, unlike a mineral,
a rock has no scientific significance except in so
far as it can be regarded as representative of the
massi from which it has been detached." T.
Crook : Min. Mag., xvii, 1913, p. 65.
Rockallite, Judd, 1897. - - A fine-grained mesocratic
soda-granite, consisting" of aBgirine-acmite, quartz,
and albite. (Rockall, N. Atlantic.)
H. S. Washington : Q.J.G.S., Ixx, 1914, p. 294.
Rock-flour. -- A general term for finely comminuted
rock-material corresponding in grade to mud, but
formed by the grinding- action of glaciers and ice-
sheets, and therefore composed largely of un-
weathered mineral particles.
Rock-series, Brogger, 1904. -- An assemblage of jg-
neous rock types irn a single district and belonging-
to a single period of igneous activity, charac-
terised by a certain community of characters,
chemical, mineral, and sometimes even textural.
A. Harker : Journ. Geol., viii, 1900, p. 389.
Rodding Structure. See Mullion Structure.
Rodingite, Bell, 1911. A coarse-grained gabbro-like
rock associated with dunite, containing dialla.o-e
and grossularite. Altered! varieties containing
prehnite and/or serpentine are recognised.
(Nelson, New Zealand.)
J. M. "Bell : Ceol. Sitrv. New Zealand, Bull.. 12, 1911. p. 31.
202 THE NOMENCLATURE OF PETROLOGY
Rodite. A brecciated achondritic meteorite composed
of bronzite and ollvine with small amounts of
olig-oclase and iron rich in nickel ; = Brecciated
Rohrbach Solution. -- A yellow aqueous solution of
barium mercuric iodide, having- a maximum
specific gravity of 3.^5.
Rosiwal's MicrometriC Method. A method of deter-
mining- the percentages (by volume) of the minerals
in a rock, bv measuring- with an eve-piece micro-
meter the linear intercepts of each mineral, as seen
in thin section along- a series of lines suitably dis-
tributed over the section. The principle of the
method was originally suggested by Delesse in
F. C. Lincoln & H. L. Rietz : Econ. Geol., viii, 1913, p. 120.
S. T. Shand : Jonrn. G"ol., xxiv, 1016, p. ?q4.
A. Johannsen & E. A. Stephenson : Journ. Geol., xxvii, iqiq,
Rougernontite. O'Neill. 1014. A phanerocrvstalline
rock containing- anorthite and titanaug-ite, with
small amounts of olivine and iron-ores.
J. J. O'Neill : Geol. Sur-v. Canada Mem., 43, (Pub. No.
1311)1 iQi4. P- 74-
Routivarite, Sjogren, 1893. A fine-grained ig-neous
rock composed of orthoclase, plag-ioclase, ouartz,
and g'arnet. (Routivara, Swedish Lapland.)
Rouvillite, O'Neill. 1914. -- A leucocratic variety of
theralite, containing about 53 per cent, of labra-
dorite, and 27 per cent, of neoheline, with small
amounts of titanaug-ite, brown hornblende, nvrite
and aoatite. (St. Hilaire, Montreal.)
J. J. O'Neill : Geol. Surv. Canada Mem., 43 (Pub. No.
1311), 1914, p. 35-
Rubble. A general term for coarse non-graded
Rudaceous, Grdbau^ 1904, = Psephitic. - - Terms
applied to sedimentary rocks composed of
coarsely-graded detritus such as gravel, shingle,
THE NOMENCLATURE OF PETROLOGY 203
Saccharoidal Texture. A granular texture, resemb-
ling that of loaf-sugar, and typically developed in
certain statuary marbles.
Sagvaildite, Rosenbusch, 1883. -- A granuiose meta-
morphic rock composed essentially of pyroxene and
Salic, C.l.P. \V ., 1906. A mnemonic term (recalling
silica and a/umina) applied to the group of stan-
dard normative minerals which includes quartz,
felspars and ^elspathoids.
Saltation, McGee, 1908. A mode of transportation of
debris by running water, in which the particles
make intermittent leaps from the bed of the
stream ; a form of movement intermediate between
rolling or sliding, and suspension.
G. K. Gilbert : U.S.G.S. Prof. Pa-p., 86, 1914, p. 15.
Sandstone. A cemented or otherwise compacted de-
trital sediment composed predominantly of quartz
grains, the grades of the latter being those of
sand. Mineralogical varieties such as lelspathic
and glauconitic sandstones are recognised, and
also argillaceous, siliceous, calcareous, ferruginous
and other varieties according to the nature of the
binding or cementing material. Corresponding
rocks composed of coarser grades have been called
grits, but the same term has also been used to con-
note angularity of grain, independently of grade-
L. Cayeux : Structure et Origine des Gres du T ertiare
parisien, Paris, 1907.
A. Holmes : British Fire Prevention Committee, Red Book,
256, 1920, p. 76.
Sandstone Dykes. A term applied to dyke-like masses
of sandstone formed by deposition in fissures from
above or by injection into earthquake-fissures from
J. S. Diller : Bull. Geol. Soc. Am., i, 1890, p. 411.
204 THE NOMENCLATURE OF PETROLOGY
Sanidinite. - - This term has been variously used for
igneous rocks composed mainly of sanidine or
other forms of alkali-felspar, whether occurring as
volcanic, phanerocrystalline, or porphyritic rocks,
or as ejected blocks, cognate enclosures, or segre-
A. Lacroix : Enclaves des Roches volcanigues, 1^93
W. H. Weed & L. V. Pirsson : Am. Journ. Sci., 1, 1893,
Santorinite, Washington t 1897. -- A leucocratic vol-
canic rock, with normative quartz and a high con-
tent of silica (about 65 per cent.), composed mainly
of plagioclase varying from labradorite to
anorthite. The same name has been applied by
Becke to hypers thene-andesites containing sodic
andesine or oligoclase, to distinguish such rocks
from alboranite. (Santorin.)
Sanukite, Weinschenk, 1890. A volcanic rock of
andesitic composition, containing crystals of
hypersthene, garnet, and a little andesine in a
glassy groundmass ; garnetiferous boninite.
Sapropelic Coals, 'Potonie, 1904. A group of coals,
including the cannel- and boghead-types., which are
largely composed of the indurated jelly-like slime
derived from macerated organic debris, and known
Samaite, Brogger, 1883. -- A variety of felspathoid-
syenite containing cancrinite and aegirine.
Saturated, Shand, 1913. A term applied to minerals
(e.g., felspars) which are capable of forming in the
presence of free silica, and extended to describe
rocks composed wholly of saturated minerals.
S. J. Shand: Geol. Mag., 1913, p. 508; 1914, p. 485; 1915,
A. Holmes : Geol. Mag., 1917, p. 115.
Saussuritisation. A term applied to processes where-
by the plagioclase felspars of dolerites and other
igneous rocks become altered by the breakdown ot
THE NOMENCLATURE OF PETROLOGY 205
the solid solution of albite and anorthite into a
dense aggregate of saussurite. This material,
originally thought to be a specific mineral, is com-
posed essentially of albite (or oligoclase) and zoi-
site (or epidote), together with variable amounts
of calcite, sericite, and calcium-aluminium silicates
other than those of the epidote group. The altera-
tion is specially characteristic of gabbros and green-
stones (epidiorite and diabase), and is accompanied
as a rule by uralitisation or chloritisation. It may
be due to auto-, contact-, or low-grade dynamic-
G. H. Williams : U.S.G.S. Bull. 62, 1890, p. 67.
Saxonite, Wads worth, 1884. A peridotite containing
orthorhombic pyroxene as the essential mineral, in
addition to olivine; = Harzburgite.
Scapolite Rocks. A general term for rocks contain-
ing scapolite irrespective of its origin as a
J. E. Spurr : Am. Journ. Sci., x, 1900, p. 310.
J. S. Flett : Summ. Prog. Geol. Surv. (1906), 1907, p. 116.
W. G. Foye : Econ. Geol., xi, 1916, p. 677.
A. Lacroix : Bull. Soc. franf. Min., 1916, p. 74.
Scapolitisatiotl. The processes whereby the alumino-
silicate minerals of igneous rocks such as gabbro
are replaced by scapolite. Plagioclase is the
mineral commonly so altered, associated augite
being changed concomitantly to hornblende.
Schalstein, Stifjt, 1825. A term for altered basaltic
and spilitic rocks and tuffs; shearing structures
(incipient schistosity and cleavage), and partial re-
placement of the rocks by calcite being characteris-
Schillerisation, ]udd, 1885. The development, along
certain planes within a mineral, of minute in-
clusions which reflect light simultaneously and so
give rise to the appearance known as " schiller. "
J. W. Judd : Q.J.G.S., xli, 1885, p. 383.
Schist. -- A general term for foliated metamorphic
rocks, the structures of which are controlled by
2o6 THE NOMENCLATURE OF PETROLOGY
the prevalence uf lamellar minerals such as micas,
chlorite, talc, and hornblende (in part), which have
normally a flaky or elongated habit ; or of stressed
minerals such as quartz and calcite, which have
crystallised in elongated forms rather than in the
granular forms generally assumed in the absence
of shear. A common characteristic of schists is
that they may be divided into folia? which are
mineralogically similar ; whereas in gneisses, alter-
nating bands or foliae are usually mineralogically
dissimilar, and the tendency to split is much less
marked. Cf. Foliation.
For References, see under Metamorphism.
Schistosity. The property of a foliated rock whereby
it can be divided into thin flakes or lenticles, the
property depending on the parallelism of the cleav-
age-planes of the lamellar minerals, such as biotite,
to which the foliation is due.
Schlieren. An old mining term applied to irregular
masses, generally streaky in form, occurring in a
body of igneous rock, from the normal type of
which they differ transitionally in texture and /or
composition. They may represent differentiation
in situ, partial assimilation of fragments of coun-
try rock, or injections of residual liquors into al-
ready crystallised material.
Schonfelsite, Uhlemann, 1909. A variety of picrite-
porphyry containing phenocrysts of olivine and
augite in an aphanitic groundmass composed of
apatite, titaniferous magnetite, bronzite, and
bytownite, in an interstitial base of brown glass
and chloride minerals.
Uhlemann : Tscherm. Mitt. Pet, Min., xxviii, 1909, p. 434.
Schorl Rock,- Boase, 1832. A Cornish term for a rock
composed essentially of aggregates of black tour-
maline (i.e., of schorl) associated with quartz.
Schriesheimite, Salomon, 1904. A variety of horn-
blende-picrite. (Schriesheim, Odenwald.)
THE NOMENCLATURE OF PETROLOGY 207
Scoptllite. A variety of crystallite consisting- of rods
or stems terminated by divergent brushes or
plumes, characteristic examples of which are found
in the Corriegills pitchstone of Arraii.
F. Rutley : Min. Mag., ix, 1891, p. 261.
Scorise. Lig"ht cellular masses of volcanic rock
Scyelite, ]udd, 1885. A hornblende-biotite-peridotite
with well-marked poikilitic texture (lustre mottling)
due to the inclusion of rounded olivines in large
crystals of other minerals.
(Loch Scye, Caithness.)
J. W. Judd : Q.J.G.S., xli, 1885, p. 401.
Sebastianite, Lacroix, 1917. - - A phanerocrystalline
rock composed of anorthite and biotite, with
smaller amounts of augute and apatite. The type
differs from puglianite, of which it is a hetero-
morphic form, in containing biotite instead of
leucite. (Mte. Somma.)
A. Lacroix : C.R., clxv, iqiy, p. 210.
Secondary. - - A general term applied to epiclastic
rocks, and to minerals formed as a consequence of
the alteration of pre-existing- minerals. Secondary
minerals may thus be formed in situ as pseudo-
morphs or paramorphs, or they may be deposited
from solution in the interstices of a rock through
which the solution is percolating. It has been
proposed to apply the terms deuteric or paulopost
(q.v.} to alterations and alteration products effected
bv processes genetically associated with those by
which the primary mineral was formed ; restricting
secondary to alterations and alteration products
effected by later processes independent of those
concerned with the genesis of the primary mineral.
For example, tourmalinisation is a paulopost pro-
cess, while lateritisation is a secondary process.
Secretions. A general term applied to all materials
which have been deposited from solution bv infil-
tration in the cavities of rocks, e.g. , amygdales.
geo&es. Cf. Concretions.
208 THE NOMENCLATURE OF PETROLOGY
Sedimentary Rocks. A general term for loose and
cemented sediments of detrital origin, generally
extended to include all exogenetic rocks (residual,
detrital, organic, and solution deposits). Cf.
E. Andree : Geol. Rnnd., ii, 1911, pp. 61, 119.
A. C. Trowbridge : Journ. Geol., xxii, 1914, p. 420.
G. M. Davies : Proc. and Trans. Croydon Nat. Jlist. a>:cl
Sci. Soc., 19115-16, p. 153.
P. G. H. Boswell : Geol. Ma?., xxvii, 1916, pp. 105, 163.
L. Cayeux : TJ Etude pe'trogra-phique des Roches sedi-
mentaires; Mem. Carte Geol. France. 1916.
E. M. Kindle : Journ. Geol., xxvii, 1910. p. -^9.
W. Deeke : Ber. Naturfor. Gesell., xxii, (i), 1910.
Seebenite, Salomon, i8q8. A variety of hornfels con-
taining felspar and cordierite as the dominant
minerals. (Seeben, near Klausen.)
Segregations. A term applied to authigenous mineral
aggregates, in masses or streaks, occurring in
igneous rocks, and representing earlv products of
crystallisation from the same respective magmas ;
= Endogenous enclosures = Cognate inclusions.
Selagite, Cordier, 1868. A variety of mica-trachyte, or
minette, characterised by abundant phenocrvsts of
bleached bietite in al groundmass of orthoclaF-e
and oligoclase laths with grains of diopside.
II. S. Washington: Am. Journ. Sci., ix, io<~~o, p. 47.
Septarian Structure. A structure developed in cer-
tain concretions known as septarian nodules, due
to an irregular polygonal system of internal
cracks, which are almost always occupied bv cal-
cite or other minerals. The structure closely re-
sembles the desiccation-structure of mud-cracks,
and is probably developed bv a similar cause
contraction due to the desiccation of the colloidal
material in the interior.
W. A. Richardson : Mln. Mag., xviii, 1919, p. 127.
Seriate Fabric, C.J.P.W., 1906. A variety of inequi-
granular texture, in which the sizes of the crystals
form a continuously graded series.
J. P. Iddings : Igneous Rocks. I, 1909, p. 196.
THE NOMENCLATURE OF PETROLOGY 209
Serialisation. The hydrothermal or other processes
whereby alumino-silicate minerals are replaced by
W. Lindgren : .Trans. Am. Inst. Min. Rng., xxx, 1900, p.
Series. A term applied to a number of related rocks
or minerals arranged, or capable of arrangement,
in a natural sequence of succession, composition
or other property; e.g., Charnockite Series, Pyro-
xene Series. Stratigraphically the term is applied
to the main subdivisions of Systems.
Serpentine. A rock made up predominantly of ser-
pentine ; generally formed by the hydrothermal
alteration of neridotites.
T. G. Bonney : Q.J.G.S., xxxiii, 1877, p. 884; Ixiv, 1908,
J. S. Flett : Mem. Geol. Surv., 359 (Lizard), 1912, p. 61.
R. P. D. Graham : Econ. Geol. xii, 1917, p. 154.
W. N. Benson: Am. Journ. Sci., xlvi, 1918, p. 693.
Serpentinisation. The process whereby magnesium-
rich minerals and rocks are altered to serpentine.
Shackanite, Daly, 1912. A variety of analcite-
(Shackan, Midway Range, British Columbia.)
R. A. Daly : Geol. Surv. Canada, Mem., 38 (Pub. 1203),
1912, p. 414.
Shale. - - A laminated sediment, in which the con-
stituent particles are predominantly of the clay
W. M. Hatchings: Geol. Mag., 1894, pp. 36, 64; 1896, pp.
Shastaite, Iddings, 1913. A general name suggested
for andesine-dacites, i.e., for normal dacites.
(Mt. Shasta, California.)
Shastalite, Wadsivorth, 1891. A term suggested for
(Mt. Shasta, California.)
Sherghottite. An achondritic meteorite mainly com-
posed of augite and maskelynite.
Shimmer-aggregate, Barrow, 1893. A micaceous
aggregate replacing altered alumino-silicate
210 THE NOMENCLATURE OF PETROLOGY
minerals such as kyanite and cordierite in meta-
G. Barrow : Q.J.G.S., xlix, 1893, p. 340.
Shingle. Loose detritus of coarser grades than those
of gravel, e.g. , having- a majority of the pebbles of
larger size than a walnut.
Shonkinite, Pirsson, 1895. A melanocratic and gener-
ally felspathoidal syenite or monzonite composed of
orthoclase, plagioclas<e and pyroxene, with a small
and variable amount of nepheline.
(Shonkin Sag, Montana.)
W. H. Weed & L. V. Pirsson : Bull. Geol. Soc. Am., 6,
1895, P- 4i5-
G. W. Tyrrell : Trans. Roy. Soc. Edin., li, 1915, p. 552.
Shoshonite, Iddings, 1895. A mafic variety of olivine-
trachydolerite, containing orthoclase-mantled
labradorite ; associated with absarokite and
banakite. (Shoshone R.. Yellowstone Park.)
J. P. Iddings : Journ. Geol., iii, 1895, p. 943.
- U.S.G.S., Mon. xxxii (ii), 1899, p. 339.
Siderite. -- A general term for meteoric irons, com-
posed almost wholly of nickel-iron, including
hexahedrites, octahedrites, and ataxites.
Siderolite, Maskelyne, 1863. - - A genera] term for
stony-iron meteorites which contain large propor-
tions of both silicates and nickel-iron. The silicate
minerals include bronzite and olivine, and, in small
amount, anorthite. Brezina has restricted the
term to include onlv the mesosiderites, lodranite,
and graham ite. Cf. Lilhosiderite.
Siderophyre, Tschermak, 1883. A siderolite contain-
ing crystals of bronzite and asmanite (tridymite) in
a network of nickel-iron.
Sieve Texture. A texture of metamorphic rocks due
to the occurrence of abundant inclusions in larger
spongv crystals ; = Diablastic.
Silcrete. Lamplugh, TQ02. - - A term suggested for
conglomerates formed bv the cementation of
superficial travels bv silica.
G. W. Larrmlugri : Geol. Mag.. 1902, p*. 575.
Silex. = Flint.
THE NOMENCLATURE OF PETROLOGY 211
Silexite, Miller, 1919. A term proposed for any body
of pure or nearly pure silica of igneous or aqueo-
igneous orig-in, which occurs as a dyke, segrega-
tion mass, or cognate inclusion.
W. J. Miller : Journ. Geol., xxvii, 1919, p. 30.
Siliceous Sinter. A solution-deposit of silica formed
from the waters of geysers and other thermal
W. H. Weed : U.S.G.S. gth Ann. Rep., 1887-8, 1890, p. 619,
Sill. A tabular sheet of igneous rock injected along
the bedding planes of sedimentary or volcanic
formations ; = Intrusive sheet.
Siltstone, Green. A very fine-grained sandstone, the
particles of which are predominantly of silt grade.
Sismondinite, Franchi, 1897.- A schist having sis-
mondine as its predominant mineral.
Sivamalai Series, Holland, 1901. A series of igneous
rocks occurring in Madras, produced by the dif-
ferentiation of a highly aluminous and alkaline
magma ; the chief rock tvpes being nepheline-,
augite-, and corundum-syenites and siliceous peg-
(Sivamalai, Coimbatore district, Madras.)
T. H. Holland : Mem. Geol. Surv. India, xxx, iqoi, D. i6q.
Skarn. An old Swedish mining term for the silicate
gangue (amphibole, pyroxene, garnet, etc.) of cer-
tain iron-ore and sulphide deposits of Archaean age,
particularly those which have replaced limestone
and dolomite. The term is used in this sense by
Fennoscandian geologists, but it has been extended
to cover analogous products of contact meta-
morphism in younger formations.
V. Goldschmidt : Die Kontaktmet amor -phase im Kristianiage.
P. Eskola : Bull. Comm. Geol. Finlande, No. 40, 1914, p. 225
Sklerooelite, Salomon, 1915. -- A term proposed for
argillaceous and allied rocks which have been in-
durated bv low-grade metamorphism. The tvpe is
more dense and massive than shale, and differs
from slate in the absence of cleavage.
W. Salomon : Geol . Rund., vi, 1915, p. 404.
212 THE NOMENCLATURE OF PETROLOGY
Skomerite, Thomas, 1911. A volcanic rock, contain-
ing- phenocrysts of augite and albite-oligoclase,
with less abundant olivine, in a felted ground-
mass, consisting- predominantly of albite.
(Skomer I., Pembroke.)
H. H. Thomas: Q.J.G.S., Ixvii, 1911, p. 175.
Slate. A general term for compact aphanitic rocks
formed from fine-grained deposits such as shales,
mudstones, or volcanic ashes, having the property
of easy fissibility along planes independent of the
original bedding, whereby they can be parted into
thin plates indistinguishable from one another in
W. M. Hutchings : Geol. Mag., 1890, pp. 264, 316; 1891,
p. 164; 1892, pp. 154, 218; 1894, pp. 36, 64.
Soda-. A prefix added to the names of igneous rocks
to indicate that they contain soda-pvroxenes and/or
soda-am phi boles ; e-g-> soda-rhyolite, soda-
trachyte, soda-granite, etc.
Sodalitite, Ussing, IQIT. A phanerocrystalline rock,
composed essentially of sodalite, with small
amounts of aeeirine, eudialvte, and alkali-felspar.
N. V. Ussing : Mfdd. om Gronland, xxxviii, 1911.
Soggendalite, Kolderup, 1896. - - A melanocratic
dolerite rich in pyroxene.
C. F. Kolderup : Bergens Mus. Aarb., 1896, p. 159.
Sol. A homogeneous suspension of colloidal matter
in a liquid. See Colloid.
Solfataric. - - A term applied to a " dormant " or
"decadent" stage of volcanic activity char-
acterised by the emission at the surface of gases
and vapours of volatile substances.
F. W. Clarke : U.S.G.S. Bull 616 (Data of Geochemistry},
1916, p. 260.
Solid Solution. A crystalline and homogeneous
solid, representing a mixture of two or more sub-
stances, and often, though not necessarilv, com-
posed of isomorphous compounds. The pro-
portions of such a mixture can change within cer-
tain critical limits without destroying the homo-
THE NOMENCLATURE OE PETROLOGY 213
geneity. Many of the common igneous rock-
forming minerals are complex solid solutions,
e.g. , felspars, pyroxenes and amphiboles ; whereas
minerals formed by the action of shearing stress
in rocks undergoing metamorphism are generally
of less complex constitution.
Solvsbergite, Brogger, 1894. -- A fine-grained hole-
crystalline rock with trachytic texture, consisting
of alkali-felspars with soda-pyroxenes and amphi-
boles. The rock is richer in mafic minerals than
bostonite and differs from grorudite by the absence
of quartz. (Solvsberg, Norway.)
W. C. Brogger : Ern-ptivgest. Kristiania, i, 1894, p. 67.
Sommaite, Lacroix, iqo$. A monzonitic rock occur-
ring as ejected blocks, containing bytownite,
orthoclase, augite and olivine, and occasionally
in small amount, leucite. Chemically the rock
corresponds with ottajanite.
(Mte. Somma, Vesuvius.)
A. Lacroix : C.R., cxli, TQO^, p. 1188.
Sondalite, Stache cV von John, 1877. A metamorphic
rock composed of cordierite, quartz, garnet, tour-
maline and kyanite.
vSonstadt Solution. See Thoulet Solution.
Sordawalite, N&denskjold, 1820. A name given to
the vitreous selvage of a dyke of olivine-dolerite ; =
WichtisitSj = Tachylyte.
(Sorclawala, L. Ladoga, Finland.)
Soret Principle. A thermo-dynamic principle, stat-
ing that if the temperature varies from point to
point in any dilute solution, the concentration of
the solute also varies, and in such a wav that
equilibrium is only established when the concen-
tration is everywhere proportional to the absolute
Sparagmite. - - A collective term for the late Pre-
Cambrian or Jotnian Scandinavian rocks, which,
like those of the Torridonian of Scotland, com-
prise polygenetic conglomerates, felspathic grits,
arkose, and graywacke*.
2i 4 THE NOMENCLATURE OF PETROLOGY
Specific Gravity. - The ratio of the mass of any
quantity of a substance to the mass of an equal
volume of some standard substance. In the case
of solids and liquids the latter is chosen as water
at 4 C. Cf. Density.
A. Holmes : Petrogra-phic Methods and Calculations, 1920.
Specific Heat. The quantity of heat necessary to raise
the temperature of one gram of a given substance
by i C.
K. Schulz : Fort, der Min. Krist. Pet., ii, 1912, p. 250;
1913, p. 273.
W. P. White: Am. Journ. Sci., xlvii, 1919, pp. i, 44.
Sperone. - - A porous variety of leucitite containing
small crystals of melanite.
Spessartjte, Rosenbusch, 1895. A diorite-lamprophyre
consisting- essentially of green hornblende and
plagioclase. The name is also used for gfarnets
which approximate in composition to Mn,AL(SiO 4 ) 8 .
Sphenolith, Burckhardt, 1906. An injected igneous
intrusion having an approximately wedge-shaped
C. Burckhardt : Cong. Geol. Inter. Guide, 26 (Mexico). 1906,
Spheroidal. See Orbicular.
Spheroidal Parting. A structure due to uniform con-
traction during cooling produced in igneous rocks
of fine homogeneous grain, and occurring as a
series of concentric spheroidal or ellipsoidal cracks
about compact nuclei. Each set of cracks is more
strong-lv developed during weathering, the succes-
sive shells so produced resembling- the layers of an
onion, and varving in diameter from an inch or
two to several feet.
Spherulite, Vogelsdng, 1872. A radiating and often
concentricallv arranged aggregation of one or
more minerals, in outward form approximating 'to
a spheroid, and due to the radial growth of pris-
matic or acicular crystals in a viscous magma
or rigid glass about a common centre or inclusion.
THE NOMENCLATURE OF PETROLOGY 215
The spherulitic body itself is said to have a radial or
concentric texture, while the rock, which may be
hemicrystalline, devitrified, or still glassy, is said
to have a spherulitic structure,
F. E. Wright : Bull. Geol. Soc. Am., xxvi, 1915, p. 255.
Spherulitic Structure. A structure in which spheru-
lites are distributed through an igneous rock or
W. Cross : Butt. Phil. Soc. Wash., xi, 1891, p. 411.
J. P. Iddings : Bull. Phil. Soc. Wash., xi, 1891, p. 445.
L. V. Pirsson : Am. J. Sci., xxx, 1910, p. 97.
Spiculite, Rutley, 1891. A spindle-shaped crystallite
considered to represent the coalescence of a linear
series of globulites ; = Belonite.
F. Rutley : Min. Mag., ix, 1891, p. 263,
Spilite, Brongniart, 1827. A basaltic rock, generally
vesicular or amygdaloidal, whose felspars have
been albitised. Pyroxene or amphibole, more or
less altered, and sometimes serpentinised olivine
may be present.
Spilitic Suite, Deivey cV Flett, 1911. -- A suite of
igneous rocks, comprising extrusions and minor
intrusions, characterised throughout by an abund-
ance of soda-felspar, and by the prevalence of
albitisation ; named after spilite, the type member
of the suite.
II. Dewey & J. S. Flett : Geol. Mag., 1911, p. 202.
J. A. Thomson : Q.J.G.S., Ixix, 1913, p. 665.
A. H. Cox : Rep. Brit. Assoc. (Birmingham, 1913), 1914? P.
Spilosite, Zincken, 1841. A contact metamorphosed
shale or slate, having a maculose structure, due to
the presence of aggregates of cryptocrystalline
matter rich in iron-oxides, in a streaked matrix of
sericite and chlorite and minute grains of quartz.
H. Dewey : Trans. Roy. Geol. Soc. Cornwall, xv, 1915,
Spotted Slates or Spotted Schists. In argillaceous
rocks, altered by contact metamorphism of low to
moderate intensity, metamorphic diffusion and dif-
210 THE NOMENCLATURE OF PETROLOGY
ferentiation about numerous centres effect partial
reconstitution convergent towards, but not neces-
sarily attaining to definite minerals. Arrested
development may be recorded in concretionary
spots of imperfectly individualised minerals (such
as andalusite, cordierite, mica or chloritoid) in a
felted base composed largely of sericitic matter.
For varieties of such spotted rocks there are no
special terms in British nomenclature, the follow-
ing German terms having been widely adopted :
Fleckschiefer. Characterised by minute flecks
or spots of indeterminate material.
Fruchtschiefer. - - Characterised by concre-
tionary spots suggestive of grains of wheat.
Garbenschiefer. Characterised by concre-
tionary spots suggestive of carraway seeds.
Knotenschiefer. Characterised by conspicuous
subspherical or polyhedral clots often com-
' posed of definitely individualised minerals.
All these types are allied to and pass into ordi-
nary varieties of hornfels and schist. Cf.
Stalactite. A pendant concretionary deposit of cal-
cium carbonate formed from percolating solutions
in icicle-like masses on the roofs of limestone
caverns and in other analogous situations.
Stalagmite. A concretionary deposit of calcium car-
bonate formed from dripping solutions on the
floors and walls of limestone caverns, and in other
Static Metamorphism, Judd, 1889. - - A variety of
regional metamorphism brought about by the
action of heat and solvents, at high pressures, the
latter being due to a superincumbent load, and not
induced by erogenic deformation.
R. A. Daly : Bull. Geol. Soc. Am., 23, 1917, p. 397.
Staurotile, Cordier, 1868. -- A variety of mica-schist
characterised by porphyroblastic crystals of stauro-
lite, often accompanied by garnet.
THE NOMENCLATURE OF PETROLOGY 217
StOCkwork. A mineral deposit, consisting of a sys-
tem of small reticulated veins (forming a com-
plicated network) traversing the country rock.
Strain-shadows. A general term for the undulatory
extinction seen in homogeneous minerals, such as
quartz, indicating a modification of the normal
optical properties due to strain. The phenomenon
is commonly seen in cataclastic rocks, and must
not be confused with the partial extinction of zoned
Strain-slip Cleavage. A variety of cleavage occur-
ring in certain low-grade metamorphic rocks, due
to differential movement or " slip " along each of a
nearly parallel series of closely-packed shear-
planes. Between each pair of shear-planes the
rocks are puckered into sigmoidal microscopic
folds, the outer limbs of which merge tangentially
into the shear-planes.
T. G. Bonney : Q.J.G.S., xlii, 1886, p. 95.
Streaky Structure. A term denoting the presence in
rhyolitic and allied rocks of numerous dark films or
lenticular veinlets, arranged parallel, or nearly so,
to the flow-surfaces, and containing minerals such
as quartz, pyrite, chlorite, sericite, carbonates,
e pi dote, and sometimes garnet. Typically
developed in the Lake District, the " streaks "
are considered to be due to deposition in and
around contraction cracks from infiltrating solu-
tions under high pressure during the solfataric
stage of the Borrowdale vulcanism.
J. F. N. Green : Min. Mag., xvii, 1915, p. 207.
Stress Minerals, Harker, 1918. -- A term suggested
for minerals such as chlorite, chloritoid, talc,
albite, epidote, amphiboles, kyanite, etc., whose
formation in metamorphosed rocks is favoured by
shearing-stress ; contrasted with anti-stress
A. Harker : Q.J.G.S., Ixxiv, 1918, p. Ixxvii.
Stromatolithic, Foye, 1916. A term, meaning
" stone layer," applied, to the banded structure of
2i8 THE NOMENCLATURE OF PETROLOGY
composite gneisses which consist of alternating-
layers of igneous and schistose rocks in sill rela-
W. G. Foye : Journ. Geol., xxiv, 1916, p. 783.
Stronalite. A name given to the cataclastic biotite-
gneisses associated at Strona with diorite-gneiss
and kinzigite. (Strona, Ivree, W. Alps.)
Structure. A term applied (a) to the morphological
features of rocks due to fracture, e.g., columnar
structure, perlitic structure ; and (b) to the appear-
ance of a heterogeneous rock in which the textures
or composition of neighbouring parts differ from
one another, e.g. , spherulitic structure, orbicular
structure, bedded structure, gneissose structure,
SEDIMENTS : H. C. Sorby : Q.J.G.S., Ixiv, 1908, p. 171.
A. C. Trowbridge : Journ. Geol., xxii, 1914,
B. Smith : Geol. Mag., 1916, p. 146.
E. M. Kindle : Geol. Mag., 1916, p. 542.
IGNEOUS ROCKS : R. B. Sosman : Journ. Geol., xxiv, 1916,
F. F. Grout : Journ. Geol., xxvi, 1918,
MKTAMURPHIC ROCKS : U. Grubenmann : Fort, der Min.
Krist. u. Pet., ii, 1912, p. 208.
Stubachite, Weinschenk, 1891. An altered diallage-
peridotite containing tremolite, talc, serpentine,
magnetite, pyrite and breunnerite in variable
amounts. By increase of serpentine the type
passes into stubachite-serpentine.
Stylolites. A term applied to parts of certain lime-
stones which have a column-like development ; the
" columns " being generally at right-angles or
highly inclined to the bedding planes, having
grooved, sutured or striated sides, and irregular
G. H. Gordon : Journ. Geol., xxvi, 1918, p. 561.
Subhedral. See Hypidiomorphic.
Sub-rang, C.I.P.W., 1902. A division of rangs
(q.v.) based (in Classes I., II. and III.) on the
THE NOMENCLATURE OF PETROLOGY 219
relative proportions of the molecules of salic K 2 O
to salic Na 2 O, roughly corresponding to the divi-
sion of rocks based on the proportions of ortho-
clase and leucite to those of albite and soda-
felspathoids. In Classes IV. and V. the sub-rangs
are based on the relative proportions of MgO to
Subsilicic, Clarke, 1911. A term suggested in place
of " basic " to connote that the rocks so described
have a silica-content leiss than 52 per cent.
Sudburite, Coleman, 1912. A variety of basalt, often
amygdaloidal and characterised by pillow struc-
ture, and in places somewhat sheared and meta-
morphosed, consisting essentially, when fresh, of
bytownite, hypersthene, augite and magnetite (15-
20 per cent.). The type is regarded as the effusive
equivalent of norite and may be uniformly fine-
grained or porphyritic. (Sudbury, Ontario.)
A. P. Coleman : Ontario Bur. Mines, zyd Ann. Re-p., xxiii,
1914, p. 215.
Suldenite, Stache & John, 1879. A variety of horn-
blende-andesite differing from ortlerite in having
an andesitic rather than a microdioritic ground-
mass. (Mte. Confinale, Tyrol.)
Sussexite, Kemp, 1892. A nepheline-porphyry, con-
sisting essentially of nepheline and/ segirine ; a
tinguaite-like rock, free from essential felspar.
Cf. nephelinite and urtite.
(Sussex Co., New Jersey.)
Sutured Texture. A texture of granulose meta-
morphic rocks, in which the individual grains meet
in irregular interlocking contacts.
Syenite, Pliny. A term originally applied to horn-
blende-granite, now connoting a phanerocrystal-
line rock composed essentially of alkali-felspars,
and one or more of the common mafic minerals,
hornblende being especially characteristic. When
quartz is present the term quartz-syenite is used.
With increase in soda-lime-felspars relative to
220 THE NOMENCLATURE OF PETROLOGY
orthoclase, the rock passes from syenite through
syenodiorite to diorite, or through monzonite to
gabbro. The rock of Syene, Egypt, is a red horn-
blende-granite ; the type syenite is that of Dresden
H. S. Washington : Am. Journ. Sci., xxii, 1906, p. 132.
Syenodiorite, 'Evans, 1916. A term based on the form
of granodiorite for rocks like the latter, but free
from quartz, i.e., for phanerocrystalline igneous
rocks intermediate in composition between syenite
and diorite. Rocks of this, kind have generally
been called monzonite, a term which should, how-
ever, be restricted to types intermediate between
syenite and gabbro. =Monzo diorite.
Syenogabbro, Johannsen, 1917. A term suggested
for quartz-free grano gabbro, i.e., for phanero-
- crystalline igneous rocks intermediate in composi-
tion between labradorite-monzonite and gabbro.
Symplektite, Lcewinson-Lessing, 1897. A secondary
intergrowth of two minerals which are interwoven
or plaited together, one of the minerals having
often a vermicular habit. The texture so pro-
duced is described as symplektitic, and is found in
certain igneous and thermally-metamorphosed
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916.
Synantetic, Sederholm, 1916. A term applied to
minerals formed between two other minerals
by interaction between the latter; as in
coronas, kelyphitic borders, reaction rims, etc.
J. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916.
Syngenetic. A term now generally applied to ore-
deposits formed contemporaneously with the
enclosing rocks, contrasting them with epigenetic
deposits of later origin than the enclosing rocks.
Syntectic, Lceivinson-Lessing, 1899 A term applied
to magmas produced by syntexis, and also used
substantively to connote the magmas themselves.
R. A. Daly : Igneous Rocks and their Origin, 1914, p. 312.
THE NOMENCLATURE OF PETROLOGY 221
Syntexis, Lcewinsqn-Lessing, 1899. The sum of the
processes whereby mag-mas are generated or aug-
mented owing to the remelting or assimilation of
portions of the lithosphere which comprise dif-
ferent classes of rocks. The term is thus of
broader scope than anatexis, which implies re-
fusion of a portion of the crust consisting- pre-
dominantly of one type 1 of rock, such as granite.
F. Loewinson-Lessing : GeoL Mag., 1911, p. 297.
System. A term applied to the sum of the phases that
can be formed from one, two (binary system), three
(ternary system), or more components under dif-
ferent conditions of temperature, pressure and
composition. Systems, or parts of systems, are
described, as shown below, in terms of their com-
Plagioclase, Albite-Anorthite : A. L. Day & E. T. Allen :
Am. Journ. Sci., xix, 1905, p. 93.
- N. L. Bowen : Am. Journ. Sci., xxxv, 1913, p. 577.
Forsterite-Silica : N. L. Bowen & O. Andersen : Am. Journ.
Sci., xxxvii, 1914, p. 487.
Diopside- Albite-Anorthite : N. L. Bowen : Am. Journ. Sci.,
xxxviii, 1914, p. 222.
Anorthite-Forsterite-Silica : O. Andersen : Am. Journ.
Sci., xxxix, 1915, p. 407.
Diopside- Albite-Anorthite : N. L. Bowen : Am. Journ. Set.,
xl, 1915, p. 161.
CaO A1 2 O 3 SiO 2 : G. A. Rankin & F. E. Wright : Am.
Journ. Sci., xxxix, 1915, p. i.
General : N. L. Bowen : Journ. GeoL Supp. Vol., xxiii,
CaO A1 2 O 3 MgO : G. A. Rankin & H. E. Merwin :
Journ. Am. Cnem. Soc., xxxviii, 1916, p. 568.
Fe 2 O 3 Fe 3 O 4 : R. B. Bosnian & J. C. Hostetter : Journ.
Am. Cnem. Soc., xxxviii, 1916, p. 807.
CaCO 3 : J. Johnston et aliter : Am. Journ. Sci., xli, 1916,
Nepheline : NaA.lSiO 4 KAlSiO 4 : N. L. Bowen: Am.
Journ. Sci., xliii, 1917, p. 115.
H 2 O K 2 SiO 3 _ SiO 2 : G. W. Morey : Journ. Am. Cnem.
Soc., xxxix, 1917, p. 1173-
MgO A1 2 O ? SiO 2 : G. A. Rankin & H. E. Merwin : Am.
Journ. Sci., xlv, 1918, p. 301.
CaO MgO SiO 2 : J. B. Ferguson & H. E. Merwin: Am.
Journ. Sci., xlviii, 1919, p. 165.
THE NOMENCLATURE OF PETROLOGY
Tachylyte, Breithaupt, 1826. A black compact glassy
rock of lustrous basaltic composition, generally
occurring as a chilled selvage in dykes and sills,
but in Hawaii exceptionally forming the bulk of
certain lava flows.
G. A. J. Cole : Q.J.G.S., xliv, 1888, p. 300.
A. Harker : Mem. Geol. Surv. Scot. (Small Isles), 1908,
Taconite. A term used in the Lake Superior district
for ferruginous cherts of Animikian age. The
rocks so designated are of various tints, and may
be finely granular, banded, or brecciated. They
represent a complete replacement of greenalite-
rock (q.v.) by silica, iron-ores, and ferruginous
C. R. Van Hise C. K. Leith : U.S.G.S., Mon. Hi, 1911, pp.
Tactite, Hess, 1919. A general term suggested for
rocks of complex mineral composition formed by
the contact metamorphism of limestone, dolomite,
and other carbonate rocks, and into which foreign
matter from the intrusion has been introduced by
hot solutions. Rocks of the enclosing zone, such
as tremolite- and wollasfonite-marbles, are not
covered by the term.
F. L. Hess : Am. Journ. Sci., xlviii, 1919, p. 377-
Tahitite, Lacroix, 1917. A variety of felspathoidal
trachyandesite containing phenocrysts of hauyne.
The rock is a microlitic form of the nepheline-mon-
zonite with which it is associated in the type-
locality. (Tahiti, Pacific.)
A. Lacroix : C.R., clxiv, 1917, p. 581.
Taimyrite, Chrouschoff, 1892. A variety of soda-
trachyte characterised by the presence of actual or
occult quartz, and regarded as the effusive equiva-
lent of nordmarkite.
THE NOMENCLATURE OF PETROLOGY 223
Talc-Schist. A schist in which talc, generally asso-
ciated with mica and quartz, is the dominant
Tamaraite, Lacroix, 1918. A melanocratic dyke rock,
containing- augite and barkevikite as the chief
mafic minerals, and nepheline, or analcite, as the
chief felsic constituent ; in addition small amounts
of orthoclase or plagioclase may be present. The
type is thus a lamprophyric facies of nepheline-
bas;alt. (Los Archipelago.)
A. Lacroix : C.R., clxvi, 1918, p. 543.
Taraspite. A mottled variety of compact dolomite of
Jurassic age, used for decorative purposes.
Taurite, Lagorio, 1897. A soda-rhyolite characterised
by the presence of aegirine, and differing from
comendite in having a spherulitic or micro-
(Near Sebastopol, Crimea.)
Tavolatite, Washington, 1908. A leucite-rich vol-
canic rock, containing large phenocrysts of leucite
in a groundmass of leucite, hauyne, and augite
with small amounts of orthoclase, labradorite and
garnet. Intermediate between leucitite on the
one hand, and leucite-trachyte or tephrite on the
other. (Tavolato, Roman district.)
H. S. Washington : Carnegie Inst. Wash., Pub. No. 57, 1906,
Tawite, Ramsay, 1894. A phanerocrystalline rock
composed essentially of sodalite and aegirine. With
the incoming of alkali-felspar the rock passes
through felspathic - tawite to sodalite-syenite.
Porphyritic rocks of the same composition are
known as Tawite-porphyry. (Kola Peninsula.)
Taxite, Lcewinson-Lessing, 1891. A general term for
volcanic rocks of clastic appearance owing to the
consolidation and aggregation of more than one
kind of product from the same flow. When the
different consolidation products are disposed in
alternating bands the resulting rock is described as
224 THE NOMENCLATURE OF PETROLOGY
eutaxite, and the structure as eutaxitic. When
the aggregation resembles a breccia, the rock is
described as ataxite, and the structure as ataxitic.
F. LoewinsonrLessing : Bull. Soc. Beige Geol., v, 1891, p.
Tectonite, Backlund, 1918. A mylonitic rock formed
from crystalline schists of sedimentary origin and
in part again recrystallised. Cf. Proiomylonite.
H. G. Backlund : Geol. For. Fork., xl, 1918, p. 198.
Tektite, Suess, 1900. A group term suggested for
moldavites, billitonites, australites, and queen-
stownites, in place of the term obsidianitc proposed
F. E. Suess : Mitt. Geol. Ges. Wien, vii, 1914, p. 54.
F. P. Mueller : Geol. Mag., 1915, p. 206.
Tephrite, Cordier, 1816. A basaltic rock containing
plagioclase and nepheline or other soda-fels-
pathoid. With the addition of olivine the rock
Tephritoid, Bilcking. -- A rock having the chemical
composition of a tephrite, but containing a soda-
rich glassy base in place of nepheline. Cf.
Terra rossa. A red ferruginous earth formed as a
residual product during the subserial denudation
of limestones, the type area of its occurrence be-
ing the Karst lands of the Adriatic.
Teschenite, Hohenegger, 1861. An alkali-rich variety
of analcite-dolerite characterised by the presence
of idiomorphic purple augite or aegirine-augite,
and generally containing soda-amphiboles such as
barkevikite. (Teschen, Bohemia.)
G. W. Tyrrell : Q.J.G.S., Ixxii, 1917, p. 84.
Mem. Geol. Surv. Scot. (East Lothian), 1910, p. 114.
Texture. The appearance, megascopic or microscopic,
seen on a smooth surface of a homogeneous rock
or mineral aggregate, due to the degree of crystal-
lisation (crystallinity}, the size of the crystals
THE NOMENCLATURE OF PETROLOGY 225
(granularity), and the shapes and interrelations of
the crystals or other constituents (fabric).
J. E. Spurr : Journ. Geol., ix, 1901, p. 586.
C.I.P.W. : Journ. Geol., xiv, 1906, p. 692.
L. Milch : Fort, der Min. Krist. u. Pet., ii, 1912, p. 163.
U. Grubenmann : Fort, der Min. Krist. u. Pet., ii 1912.
Theralite, Rosenbusch, 1887. -- A phanerocrystalline
rock composed essentially of labradorite, nepheline
and purple augite, and often containing soda-
amphiboles and biotite, or both. Analcite may
be present, and most examples are olivine bearing.
G. W. Tyrrell : Geol. Mag., 1912, p. 79.
A. Lacroix : C.R., clxx, 1920, p. 20; Geol. Mag., 1920, p.
Thermal Metamorphism. A variety of meta-
morphism in which recrystallisation is due to high
temperature, the latter not being a consequence of
dynamic processes, or of the introduction of mag-
For References see under Metamorphism.
Thin Sections. Flakes or slices of a rock or mineral
which have been ground down until their thick-
ness is reduced to nearly a thousandth of an inch,
and mounted on object-glasses for microscopic in-
vestigation. For most purposes the thickness of
the finished section should be about 30 microns
(30 ^=0.03 mm.).
H. J. Grayson : Proc. Roy. Soc. Victoria, xxiii, 1910, p. 65.
G. F. H. Smith : Min. Mag., xvi, 1913, p. 317.
A. Holmes : Petrogra-phic Methods and Calculations, 1920.
Tholeiite, Steininger, 1840. A term applied to
porphyritic basalts characterised by the presence
of phenocrysts of labradorite or bytownite in an in-
ter sertal groundmass containing glass and occult
free silica. (Tholei Schaumberg.)
G. W. Tyrrell : Geol. Mag., 1917, p. 350.
Thoulet Solution. A yellowish green transparent
aqueous solution of potassium mercuric iodide,
having a maximum specific gravity of 3.19. Also
known as Sonstadt Solution.
226 THE NOMENCLATURE OF PETROLOGY
Tilaite, Duparc & Pearce, 1905. A melanocratic
variety of olivine-gabbro or olivine-eucrite contain-
ing pyroxenes and olivine with subordinate felspar
(bytownite to anorthite) and small amounts of
hornblende, biotite, apatite and magnetite.
(Tilai Kamen, N. Urals.)
L. Duparc P. Pamfil : Bull. Soc. Min. France, xxxiii,
1910, p. 358.
Tillite, Penck. A term applied to consolidated
boulder-clays formed during glacial epochs
anterior to that of the Pleistocene.
A. P. Coleman : Bull. Geol. Soc. Am., xix, p. 347.
Smithson. Ref. (1916), Pub. No. 2458, 1917, p. 264.
Timazite, Breithaupt. A variety of greenstone con-
taining white felspar, hornblende, and in some
varieties quartz ; considered to be an altered deriva-
tive from augite-dacite or augite-andesite.
Tinguaite, Roscnbusch, 1887. A dyke rock, often
porphyritic, having the composition of an aegirine-
phonolite, and differing from solvsbergite by the
presence of nepheline.
(Serra de Tingua, Brazil.)
W. C Brogger : Eru-ptivgest. Kristiania, i, 1894, p. 109.
Tjosite, Brogger , 1898. -- A porphyritic syenite-
lamprophyre containing augite, olivine, apatite,
and magnetite in a matrix of anorthoclase laths.
Cf. Kvellite. (Kirchspiel Tjose, Laurvik.)
Toadstone. An old local name for the contemporane-
ous amygdaloidal basalts of the Carboniferous
Limestone of Derbyshire. The name either sug-
gests a resemblance between the amygdales and
the spots of a toad's skin, or is an anglicised
variant of todtstein, in reference to the absence of
H. H. Arnold-Bemrose : Q.J.G.S., Ixiii, 1907, p. 241.
Toellite, Pichler, 1873. A variety of porphyrite con-
taining phenocrysts of biotite, hornblende, and
garnet with some of andesine and quartz, in a
microgranophyric groundmass ; = Tollite.
THE NOMENCLATURE OF PETROLOGY 227
Tonalite, v. Rath, 1864. A quartz-diorite containing
hornblende and biotite as the chief mafic minerals.
Tdnsbergite, Brogger, 1890. -- A red laurvikite-like
rock, in which the felspars are orthoclase and
andesine. Some varieties are porphyritic.
(Tonsberg, S. Norway.)
Topazoseme, Haily, 1822. A rock composed essen-
tially of topaz, quartz, and tourmaline.
Topsailite, Lacroix, 1911. A lamprophyric rock (in-
termediate in type between camptonite and
kersantite), containing- phenocrysts of plagioclase
(about An 50 ), augite, apatite, and titanoferrite, in
a groundmass composed of andesine, biotite,
barkevikite, augite and sphene.
(C. Topsail, Los Is.)
A. Lacroix : Nouv. Arch, du Mus. de Hist. Nat., 5 (iii),
IQII, p. 78.
Torbanite, Liversidge, 1881. An extreme variety of
oil-shale, containing some 70 to 80 per cent, of
carbonaceous matter, including an abundance of
spores. It is a dark-brown substance, having a
dull lustre, a yellow-fawn streak and a low specific
gravity 1.2 to 1.3.
Mem. Geol. Surv. Scot. (Oil Shales of the Lothians), and
Ed., 1912, p. 159.
H. R. J. Conacher : Trans. Geol. Soc. Glasgow, xvi, 1917,
Tordrillite, Spurr ) 1900. A hololeucocratic variety of
rhyolite, characterised by the absence of mafic
minerals, and corresponding chemically to alaskite.
(Tordrillo Mts., Alaska.)
Toscanite, Washington, 1897. A variety of quartz-
trachyandesite ; i.e., a volcanic rock intermediate
in its characters between rhyolite and dacite.
H. S. Washington : Journ. Geol., v, 1897, p. 37.
Tourmaline-corundum Rocks, Scrivenor, 1910.
Very hard and fine-grained rocks of blue-black
colour, having the mineral composition indicated
22 8 THE NOMENCLATURE OF PETROLOGY
by their name. Under the microscope they show
oolitic structure, indicating that they are probably
due to the intense metamorphism of oolitic cherts
by granite. (Kinta, Malay States.)
J. B. Scrivenor : Q.J.G.S., Ixvi, IQIO, p. 435.
W. R. Jones : Q.J.G.S., Ixxii, 1916-17, p. 178.
Tourmalinisation. A term applied to the processes,
late-magmatic or pneumatolytic, whereby pre-
existing minerals or rocks are replaced wholly or
in part by tourmaline.
J. S. Flett : Mem. Geol. Surv. 347 (Bodmin and St. Austell),
1909, p. 65.
C. E. Tilley : Trans. Roy. Soc., S. Australia^ xliii, 1919,
P- i5 6 -
Trachyandesite, Michel-Levy, 1894. A general term
for rocks intermediate between trachyte and
andesite, and generally containing phenocrysts of
oligoclase or andesine in a trachytic groundmass,
the felspar microlites of which are potash
H. S. Washington : Journ. Geol., v, 1897, p. 367.
Trachybasalt, Boricky, i^^. = Tephrite (in part),-
monchiquite (in part).
Trachydolerite, Abich, 1841. - - A general term for
trachytic rocks containing labradorite in addition
to orthoclase, or basaltic rocks containing ortho-
clase in addition to labradorite; i.e., for rocks in-
termediate in character between trachyte and
H. S. Washington : Journ. Geol., v, 1897, p. 350.
Trachyte, Brongniart, 1813. -- An aphanitic volcanic
rock, generally porphyritic, containing alkali-
felspars, and one or more mafic minerals, of which
biotite and augite are those most usually
G. W. Tyrrell : Proc. Roy. Soc. Edin., xxxvi, 1917, p. 288.
Mem. Geol. Surv. Scot. (East Lothian), 1910, p. 127.
Trachytic Texture. A texture in which neighbour-
ing felspar laths of a microlitic groundmass have
a sub-parallel disposition, corresponding to the
THE NOMENCLATURE OF PETROLOGY 229
stream lines of the nearly consolidated lava or
Trachytoid Phonolite. A general term for varieties
of nepheline-phonolite, containing preponderant
alkali-felspars, and consequently having a trachytic
texture ; contrasted with nephelinitoid phonolite
in which nepheline is the preponderant felsic
Trachytoid Texture. A texture in which the pris-
matic felspars of a phanerocrystalline rock have a
parallel or sub-parallel disposition, as for example
in many varieties of alkali- and nepheline-syenites.
Traction, Gilbert, 1914. A general term for that
mode of transport of debris by running water, in
which the particles are swept along close to the
bed of the stream by rolling, sliding, or saltation ;
contrasted with suspension.
G. K. Gilbert : U.S.G.S. Prof. Pa-p., 86, 1914, p. 15.
Trap. An old Swedish name originally applied to
igneous rocks which were neither coarsely crystal-
line, like granite, nor cellular and obviously vol-
canic, like pumice and scoria. The rocks so
designated included basaltsi, dolerites, andesites,
and porphyrites (types often grouped as whin-
stones) ; altered varieties of some of these, such
as epidiorite and diabase (types grouped as green-
stones) ; and, finally, the mica-traps or lampro-
Trap-shotten Gneiss, King & Foot, 1864. A term
applied to gneiss impregnated with nearly black in-
durated material originally supposed to be in-
jections of "trap" rock, but now identified with
" flinty crush-rock." Cf. Pseudo-tachylyte.
T. H. Holland : Mem. Geol. Surv. India, xxviii, 1900, pp.
Trass. A local Italian name applied to pumiceous
tuffs which are utilised for the manufacture of
Travertine. A variety of calcareous tufa, of light
colour, often concretionary and compact, but vary-
230 THE "NOMENCLATURE OF PETROLOGY
ing- considerably in structure, some varieties being
extremely porous. Cf. Onyx Marble.
W. H. Weed : U.S.G.S. gth Ann. Ref., 1887-8, 1890, p. 619.
Trichite, Zirkel, 1873. A thin filament or hair-like
form of crystallite, often occurring- in irregular or
" F. Rutley : Min. Mag., ix, 1891, p. 263.
Tripoli, WaUeriuS t 1747. -- A fine powdery siliceous
deposit composed of the tests of diatoms and
Troctolite, v. Lasaulx, 1875. A phanerocrystalline
rock composed essentially of labradorite or bytown-
ite and olivine (always more or less serpentinised),
with little or no augite. Cf. Ossypite.
T. G. Bonney : Geol. Mag., 1885, p. 439.
J. S. Flett : Mem. Geol. Surv. 359 (Lizard), 1912, p. 85.
Trowlesworthite, Worth, 1884. A pneumatolytic
modification $>f granite containing orthoclase, tour-
maline and fluorspar with residuary quartz.
Tsingtauite, Koto, 1909. A variety of granite-
porphyry having- phenocrysts of orthoclase in a
fine-grained granitic groundmass.
B. Koto : Journ. Col. Sci. Tokyo, xxvi, 1909, p. 186.
Tufa. A porous, concretionary or compact formation
of calcium carbonate deposited around springs.
Tuff. A rock formed of compacted pyroclastic frag-
ments, some of which can g-enerally be distin-
guished as such by the naked eye. If the larger
fragments exceed the size of walnuts the rock be-
comes an agglomerate, or a volcanic breccia.
According as the prevalent constituents are frag-
ments of crystals, rocks or glass, crystal, lithic and
vitric types of tuffs are recognised. Cf. Ash.
L. V. Pirsson : Am. Journ. Set., xl, 1915, p. 191.
J. F. N. Green : Proc. Geol. Assoc., xxx, 1919, p. 165.
Tuffite, Miigge, 1893. A general term for composite
clastic rocks, in which both volcanic (pyroclastic)
THE NOMENCLATURE OF PETROLOGY 231
and detrital (epiclastic) materials are present in
TllSCUlite, Cordier, 1868. A variety of melilite-
leucitite containing- only small amounts of pyrox-
ene, ilmenite, and felspar.
Typomorphic, Becke. -- A term applied to minerals
characteristic of the particular set of physical con-
ditions which controlled their formation.
Uintaite. A black lustrous variety of bitumen having
a conchoidal fracture, and thus resembling manjak.
It differs from albertite by being- completely soluble
in turpentine, and, partly so, to the extent of 45
per cent., in alcohol ; Gilsonite.
(Uintah Co., Utah.)
G. H. Eldridge : U.S.G.S. 22nd Ann. Re-p., Pt. i, 1901, pp.
Ulrichite, Marshall, 1906. A somewhat melanocratic
variety of tinguaite containing large phenocrysts
of alkali-felspars, nepheline, and soda-pyroxenes
and amphiboles, with smaller phenocrysts of olivine
P. Marshall : Q.J.G.S., Ixii, 1906, p. 397.
A. Holmes : Geol. Mag., 1915, p. 366.
Ultrabasic Rocks, Judd, 1881. -- A general term ap-
plied to igneous rocks containing little or no fel-
spar, but characterised essentially by one or more
of the common mafic minerals, such as olivine,
pyroxenes, amphiboles, etc. Chemically, ultra-
basic rocks have been described as those having a
percentage of silica less than that of anorthite, the
limiting fig-ure being about 45 per cent.
Ultrametamorphism, Holmquist, 1909. A general
name for processes of so extreme a character that
232 THE NOMENCLATURE OF PETROLOGY
the rocks affected pass wholly into a magmatic
condition. Cf. assimilation^ anatexis, palin-
Ultra-mylonite, Quensel, 1916. A variety of mylonite
in which primary structures and porphyroclasts
have been entirely obliterated, so that the rock be-
comes homogeneous and aphanitic with little sign,
if any, of parallel structure ; = Flinty crush-rock.
P. Quensel : Bull. GeoL Inst, U$sala, xv, 1916, p. 103.
Umptekite, Ramsay, 1894. A variety of alkali-syenite
composed essentially of alkali-felspars and soda-
amphiboles. (Umptek, Kola Peninsula.)
P. Quensel : Bull. Geol. Inst. U-psala, xii, 1914, p. 142.
Unakite, Bradley, 1874. A variety of granite contain-
ing quartz, pink felspar and green epidote.
(Unaka Range, N. Carolina.)
T. L. Watson : Am. Journ. Sci., xxii, 1906, p. 248.
Uncompahgrite, Larsen. A term applied to an ex-
tremely coarse-grained rock, containing 70 per
cent, or more of melilite, with small amounts of
pyroxene, magnetite, perovskite, and apatite.
E. S. Larsen & J. F. Hunter : Journ. Wash. Acad. Sci., iv.
iQH, P- 473-
Undersaturated, Shand, 1913. - - A term applied to
rocks wholly or partly composed of unsaturated
minerals; e.g., felspathoids and olivine.
S. J. Shand: Geol. Mag., 1913, p. 313; 1915, P- 34-
A. Holmes : Geol. Mag., 1917, p. 124.
Unequal Pressure. See Directed Pressure.
Ungaite, ladings, 1913. A general name suggested
for oligoclase-dacites. (Unga Is., Kamchatka.)
Unsaturated, Shand, 1913. A term applied to mine-
rals (e.g., felspathoids and olivine) which do not
normally occur in association with free silica ; also
applied to rocks which contain only unsaturated
minerals. (For references see Undersaturated.)
THE NOMENCLATURE OF PETROLOGY 233
Uralitisation. - - The processes whereby the primary
pyroxene of igneous rocks is altered to uralite, a
form of secondary hornblende paramorphic after
augite, and generally, but not necessarily fibrous.
G. H. Williams : U.S.G.S., Bull. 62, 1890, p. 52.
L. Duparc & T. Hornung : C.R., cxxxix, 1904, p. 223.
Urbainite, Warrzn, 1912. A facies of ilmenitite con-
taining from 10 to 20 per cent, of rutile, and from
3 to 5 per cent, of sapphirine.
(St. Urbain, Quebec.)
C. H. Warren : Am. Journ. Sci., xxxiii, 1912, p. 275.
Ureilite, Jerofejeff & Latschinoff, 1888. A coarse-
grained achondritic meteorite composed of olivine
and augite enclosed in a fine mesh of nickel-iron
with carbonaceous matter (including diamond).
The type is practically equivalent to a pallasite with
less than 10 per cent, of nickel-iron.
Urtite, Ramsay, 1896. - - A phanerocrystalline rock
composed of nepheline (85 per cent.), aegirine (12
per cent.), and accessory apatite.
(Lujaur Urt, Kola, Finland.)
W. Ramsay : G eol. For en i Stockholm Forhandl., xviii, 1896,
p. 463 ; Fennia, xv, 2, p. 22.
Vadose, Posepny, 1894. A term applied to seepage
waters occurring below the surface and above the
water-table ; contrasted with phreatic, which refers
to the ground-water below the water-table.
R. A. Daly : Econ. Geol., xii, 1917, p. 494.
Valbellite, von Schaever, 1898. A fine-grained variety
of peridotite composed of olivine, hypersthene, and
hornblende ; pyrrhotite is locally an abundant con-
stituent ; = Hornblende-harzburgite.
(Val Bella, Piedmont.)
Vallevarite, Gavelin, 1915. A somewhat leucocratic
monzonitic rock composed largely of andesine-
234 THE NOMENCLATURE OF PETROLOGY
microcline-antiperthite, with small amounts of
diopside, biotite, titanoferrite and apatite.
A. Gavelin : Geol. For. i Stockholm Fork., xxxvii, 1915,
Van der Kolk Method. A microscopic method for
determining whether the refractive index of a
mineral grain is higher or lower than that of a
liquid medium in which it is immersed and viewed.
Light rays from below the stage are cut off by in-
serting a suitable obstacle, and as the grain acts as
a lens, and the eyepiece inverts, the image, a
shadow appears (a) on the same side as the
when the grain has the higher refractive index,
(b) on the opposite side when the grain has the
J. L. C. Schroeder van der Kolk : Tabellen zur mikrosco-
pischen Bestimmung der Mineralien nach ihrem Brech-
nungsindex. Wiesbaden, 1906.
Variation Diagram. -- A graphical representation of
the variation in composition of the members of a
series of related igneous rocks; e.g. , by plotting
the bases as ordinates against silica as abscissae.
A. Marker : Nat. Hist. Ig. Rocks, 1909, p. 119.
H. H. Robinson : U.S.G.S. Prof. Pa-p., 76, 1913, figs. 32-5.
H. C. Richards : Proc. Roy. Soc. Queensland, 1916, p. 200.
A. Holmes : Q.J.G.S., Ixxii, 1916-17, p. 264.
Variolite, Aldrovande, 1648. -- An aphanitic basaltic
or andesitic rock containing numerous felspathic
spherulites with radial texture (varioles).
G. A. J. Cole & J. W. Gregory : Q.J.G.S., xlvi, 1890, p. 295.
G. W. Tyrrell : Trans. Geol. Soc. Glasgow, xiv, 1912, p. 291.
Variolitic Structure. A structure akin to spherulitic
structure occurring in basaltic rocks and especially
in the tachylytic margins of small intrusions and in
certain varieties of pillow-lavas known as variolites.
In some cases the spherulites are made up of
minute radiating fibres of plagioclase with inter-
stitial glass, and in others they are less regular and
consist of interferent sheaf-like groups of labra-
THE NOMENCLATURE OF PETROLOGY 235
dorite rods diverted by grains of augite, olivine, or
A. Harker : Nat. Hist. Ig. Rocks, 1909, p. 275.
Varnsingite, Sobral, 1913. -- A coarse-grained dyke-
rock essentially composed of albite and augite,
with accessory sphene, apatite, and magnetite ;
regarded as a pegmatoid derivative from a gabbro
magma. (Nordringa District, Sweden.)
Vaugnerite, Fournet, 1836. A variety of quartziferous
monzonite characterised by an unusual abundance
of biotite and apatite. (Vaugneray, France.)
A. Lacroix : Bull. Soc. franf. Min., xl, 1917, p. 158.
Vein. An irregular sinuous, igneous injection, or a
tabular body of rock formed by deposition from
solutions rich in water or other volatile substances.
Vein-quartz. A rock of pegmatitic or hydrothermal
origin consisting essentially of interlocking sutured
crystals of quartz, the individuals varying widely in
Venanzite, Sabatini, 1898. A holocrystalline porphy-
ritic rock occurring as a lava flow, composed of
phenocrysts of olivine and phlogopite in an apha-
nitic groundmasis of these minerals, together with
melilite, leucite and magnetite. Rosenbusch gave
the name Euktolite to this rock, not knowing that
it had already been described.
(San Venanzo, Umbria.)
Verite, Osann, 1889. A black lamprophyric pitchstone
containing crystals of phlogopite or biotite, augite,
and olivine, with little or no modal felspar; the
chemical composition is similar to that of the
melanocratic trachytes and minettes.
(Vera, Cabo de Gata, Spain.)
Vermicular Quartz. A term applied to quartz occur-
ring in worm-like forms intergrown with or pene-
trating felspars ; = quartz de corrosion.
}. J. Sederholm : Bull. Comm. Geol. Finlande, No. 48, 1916,
236 THE NOMENCLATURE OF PETROLOGY
VeSUVite, Lacroix, 1917. A variety of leucite-tephrite
rich in leucite. (Vesuvius.)
A. Lacroix : C.R., clxv, 1917, p. 482.
Vicoite, Iddings, 1915. A variety of leucite-tephrite
characterised by the presence of orthoclase ; = leu-
cite-shoshonite. (Vico Volcano, Italy.)
J. P. Iddings & E. W. Morley : Journ. GeoL, xxiii, 1915,
P- 2 34-
Vintlite, Pichler, 1875. A porphyritic variety of horn-
blende-dolerite containing phenocrysts of labra-
dorite or bytownite and brown hornblende in a
fine-grained groundmass of felspar and horn-
blende, with a little quartz.
(Vintl, near Klausen, Tyrol.)
Viridite, Vogelsang, 1872. -- A general term for ob-
scure green alteration products (including chloritic
minerals, serpentine, etc.), which cannot be, or
have not been specifically diagnosed.
Viscosity. - - Any resistance to deformation that
involves dissipation of energy by internal friction.
Viscosity of Fluids. The property of imperfect fluids
whereby they resist the action of a shearing stress ;
measured by the shearing stress required to cause
flow at a certain constant rate.
F. F. Grout : Journ. Geol., xxvi, 1918, p. 485.
A. L. Field & P. H. Royster : Trans. Am. Inst. Min. Eng.,
Iviii, 1918, p. 658.
Viterbite, Washington, 1906. -- A variety of leucite-
trachyte containing abundant large phenocrysts of
leucite. (Viterbo, Italy.)
H. S. Washington : Carnegie Inst. Wash., Pub. No. 57
(Roman Comagmatic Region], 1906, p. 35.
Vitrain, Slopes, 1919. A term suggested for the
vitreous variety of " bright " coal. In bituminous
coals it occurs as narrow, compact brilliant bands
which break into small cube-like pieces or into irre-
gular fragments with conchoidal fracture. The
fine banding characteristic of clarain is not
developed in vitrain, which, under the microscope,
THE NOMENCLATURE OF PETROLOGY 237
is seen to be uniform and structureless, the colour
in thin sections being- from yellow to amber.
M. C. Stopes : Proc. Roy. Soc. B., xc, 1919, p. 475.
Vitric Tuffs, Pirsson, 1915. Volcanic tuffs or ashes
mainly composed of comminuted fragments of
glass. Cf. lithic and crystal tuffs.
L. V. Pirsson : Am. Journ. Sci., xl, 1915, p. 191.
Vitro-. A prefix added to the names of rocks to in-
dicate the presence of abundant glass, e.g., Vitro-
basalt ; = hyalobasalt.
Vitrophyre, Vogelsang, 1867. -- A general term for
porphyritic rocks having the composition of quartz-
porphyry or orthophyre, but differing- from these
by the possession of a glassy groundmass.
Vogesite, Rosenbusch, 1887. A syenitic lamprophyre
of which the mafic minerals are generally horn-
blende, and sometimes augite, the dominant fel-
spar being oligoclase or andesine when sufficiently
fresh to be determined. (Vosges.)
W. Cross : U.S.G.S., Prof. Pa-p., goC, 1914, p. 21.
Volatile Fluxes, Evans, 1910. A general term for the
volatile constituents of magmas.
T. C. Chamberlain : Carnegie Inst. Washington, Pub. No.
A. L. Day & E. S. Shephard : Bull. Geol. Soc. Am., xxiv,
!9*3> P- 573-
Volcanic Dome. A volcanic form consisting of
rounded masses of viscous lava squeezed out from
the orifice, or of portions of older lavas or ejecta-
menta elevated by the pressure of new lava rising
from beneath. The term dome is also applied as
a geographical term to volcanic mountains of the
type of Mauna Loa.
A. Lacroix : La montagne Pelee et ses eruptions, 1906, p.
no; La montagne Pelee a-pres ses eruptions, 1908, p. 31,
S. Powers : Am. Journ. Sci., xlii, 1916, p. 261.
Volcanic Mud and Sand. Deposits occurring around
volcanic oceanic islands and coast-lines. The
deposits near shore contain fragments of volcanic
rocks and minerals, and are referred to as sands,
238 THE NOMENCLATURE OF PETROLOGY
while further out the finer particles and alteration
products form clayey or chloritic muds.
J. Murray & A. F. Renard : " Challenger " Rep. (Deep Sea
Deposits), 1891, p. 240.
Vokanite, Hobbs, 1893. A volcanic rock composed
essentially of anorthoclase and augite, and having
the chemical composition of dellenite.
(Volcano, Lipari Is.)
W. H. Hobbs : Bull. Geol. Soc. Am., v, 1893, p. 598.
A. Lacroix : C.R., cxlvii, 1908, p. 1491.
Volhynite, Ossovski, 1885. A variety of quartz-
kersantite containing- phenocrysts of plagioclase
and hornblende, with or without biotite, in a
groundmass of quartz and felspar with abundant
chlorite. (Volhynia, Russia.)
Vug or Vugh. A mining term for an unfilled cavity
in a vein, generally with a mineral lining of dif-
ferent composition from that of the immediately
Vulsinite, Washington, 1896. A variety of trachy-
andesite, similar to banakite, but somewhat richer
(Bolsena, Vulsinian district, Italy.)
H. S. Washington : Journ. Geol., iv, 1896, p. 55.
Wacke. An old term for a dark green to brownish
black earth or clay formed as the final residual
decomposition product of basaltic rocks and tuffs.
Weathering. The destructive alteration and decay of
rocks by exogenetic processes acting at the surface
and down to the depth to which atmospheric oxy-
gen can penetrate.
G. P. Merrill : Rocks, Rock Weathering and Soils, 1906.
E. Steidtmann : Econ. Geol., iii, 1908, p. 381.
J. W. Evans: Proc. Geol. Assoc., xxiv, 1913, p. 245; xxv,
1914, p. 229.
E. Weinschenk (Trans, by A. Johannsen) : Fundamental
Principles of Petrology, 1916, p. 73.
THE NOMENCLATURE OF PETROLOGY 239
Websterite, Williams, 1890. A variety of pyroxenite
composed of both monoclinic and orthorhombic
Wehrlite, Kobell, 1839. A variety of peridotite con-
taining diallage. The name is now extended to
include with diallage all other varieties of mono-
M. E. Schuster : Geognost, Jahresheft, xviii, 1907, p. 43.
Weiselbergite. A variety of micro-porphyritic
dolerite having a microlitic texture resembling that
of augite-andesite. Crystals of labradorite,
augite, and iron-ores are embedded in a ground-
mass composed of plagioelase and augite microlites
with interstitial glass.
(Weiselberg, Nahe District.)
Welded Dykes, Weinschenk. A term applied to peg-
matitic and aplitic dykes, the boundaries of which
have been obliterated by continued growth of the
minerals of the granite into which the dykes have
Wennebergite, Schuster, 1905. A variety of quartz-
iferous porphyry characterised by phenocrysts of
orthoclase, biotite, and quartz, in a microcrys-
talline and chloritic groundmass containing abun-
dant apatite and sphene. (Wenneberg, Ries.)
Whinstone. A popular general name for dark col-
oured rocks such as dolerite, basalt, porphyrite,
andesite, etc., which are comparatively unaltered,
intrusive or interbedded, have a crystalline texture
not usually coarse, and are composed of the
minerals felspar, pyroxene, and iron-ores, with or
without hornblende or olivine. As a trade-name,
it is recommended by the British Engineering
Standards Association that the term whinstone
should be strictly confined to rocks which come
under the trade heading of basalt. According to
the same authority the latter includes basalt,
diabase, dolerite, epidiorite, greenstone, lampro-
2 4 o THE NOMENCLATURE OF PETROLOGY
phyre, spilite, and teschenite. According to this
usage whinstone is made to cover both whinstones
and greenstones, and includes types which collec-
tively have usually been known as trap-rocks. Cf.
A. Holmes : Geological and Physical Characters of Concrete
Aggregates, B.F.P.C. " Red Book," 256, 1920, p. 40.
Wichtisite. A modification of dolerite rich in glass
occurring as selvages in sills or dykes or as small
(Wichtis, near Helsingfors, Finland.)
Wilsonite. A rhyo-andesite tuff containing fragments
of pumice and andesite in a matrix consisting of
shreds of glass in a granular isotropic base. The
rock has also been interpreted as a brecciated
rhyolite flow, but the evidence appears to be against
this view. (Owharoa, Hauraki, N.Z.)
Geol. Surv. N . Zealand, Bull. 16, 1913, p. 70.
Windsorite, Daly, 1903. A leucocratic variety of
quartz-monzonite, containing a small percentage of
biotite. (Windsor, Vermont.
R. A. Daly : U.S.G.S. Bull., 209, 1903, p. 45.
Woodendite, Skeats & Summers, 1912. A variety of
orthoclase-bearing basalt resembling absarokite.
E. W. Skeats & S. Summers : Geol. Surv. Victoria, Bull.
24, 1912, p. 31.
Wurtzilite. A massive, black, elastic bituminous sub-
stance, having a brilliant lustre and a conchoidal
fracture. It differs from members of the asphaltite
group not only in its elasticity, but also in resist-
ing the usual solvents.
Wyomingite, Cross, 1897. A porphyritic dyke-rock
with phenocrysts of phlogopite in an aphanitic
groundmass containing leucite and diopside ;
= phlogopite-leucite. (Wyoming.)
W. Cross: Am. Journ. Set., iv, 1897, p. 120.
THE NOMENCLATURE OF PETROLOGY 241
Xenoblast, Becke, 1903. A term applied to crystals
which have grown during metamorphism without
the development of their characteristic faces. Cf.
Xenocryst, Sollas, 1894. A term applied to allo-
thigenous crystals, generally corroded, that are
foreign to the igneous rock in which they occur.
Xenolith, Sollas, 1894. A term applied to allothi-
genous rock fragments that are foreign tO' the ig-
neous rock in which they occur ; = accidental in-
clusion, = exogenous enclosure, enclave enallo-
A. Harker : Mem. Geol. Surv. (Tert. Ig. Rocks Skye), 1904,
P- 35 1 -
Yamaskite, Young, 1906. A medium or fine-grained
rock composed of basaltic hornblende and titan-
augite, with a small amount of anorthite, and
accessory iron-ores and biotite ; olivine-bearing
varieties are also known.
(Mt. Yarnaska, Quebec.)
J. J. O'Neill : Geol. Surv. Canada, Mem., 43 (Pub. No.
1311), 1914, p. 64.
Yatalite, Benson, 1908. A pegmatoid rock (associated
with a titaniferous series of diopside-syenites
and diorites) containing as its chief constituent
uralitic actinolite (after diopside) with poikilitic
inclusions of magnetite and sphene. The other
minerals present are albi.te with microcline titani-
ferous magnetite, apatite and sphene.
W. N. Benson : Trans, and Proc. Roy. Soc. S. Australia,
xxxiii, 1909, p. 126.
Yentnite, Spurr, 1900. A coarse-grained granitoid
rock essentially containing primary scapolite,
242 THE NOMENCLATURE OF PETROLOGY
plagioclase (oligoclase-andesine), and biotite ;
= scapolite-belugite. (Yentna R., Alaska.)
J. E. Spurr : Am. Journ. Sci., x, igoo, pp. 310-15.
Yogoite, Weed, & Pirsson, 1895. A melanocratic
facies of syenite containing augite and orthoclase,
with smaller amounts of biotite and oligoclase-an-
desine. (Yogo Peak, Montana.)
W. H. Weed & L. V. Pirsson : Am. Journ. Sci., 1, 1895,
p. 472; li, 1896, p. 351.
Zeolitisation, Lacroix, 1896. - - The process whereby
the felspars and other alumino-silicates of a rock
are transformed into zeolites.
A. Lacroix : Min. de la France, ii, 1896, p. 45.
Zobtenite, Roth, 1887. A variety of gabbro-gneiss
containing knots or eyes of diallage surrounded by
streams of uralite and embedded in a granular
mass of epidote and plagioclase (saussurite).
Zoning. A term applied to the structure of a mix-
crystal which is composed of isomorphous com-
pounds arranged in layers or zones of different com-
position ; successive zones having been deposited
from a magma (or other liquid solution), which
gradually changed in composition owing to the
separation of crystal phases.
N. L. Bowen : Am. Journ. Set., xl, 1915, p. 180, and Journ.
Geol. Su-p-p., vol. xxiii, 1915, p. 38.
2 4 3
FRENCH PETROGRAPHIC TERMS
Affleurement, outcrop ; exposure.
Agents mineralisateurs, mineral-
Agregees (Roches} , clastic
Aiguille, needle (acicular min-
eral) ; spine (e.g. of Mount
Alluvion aurifere, placer.
Amphlgenite (Cordier, 1868),
leucite-tephrite and other
basaltic rocks containing
Anagenite, conglomerate formed
of fragments of granite, gneiss
Ancienne (eruptive), term ap-
plied to pre-Tertiary igneous
Anorthose, plagioclase (Celesse);
now used for anorthoclase.
Arendalite, garnet rock.
Argile smectique, Fuller's earth.
Btonnee (structure) , mortar
Boue, mud; ooze.
Boules (division en), spheroidal
partings in igneous rocks.
Bulle, gas bubble, in inclusions
Cargneule, cellular dolomite.
Chaille, siliceous concretion.
Cheires, flows of block-lava ; =
Chevauchement, overfold, thrust.
Cicatrisation, healing of broken
or corroded crystals by a
secondary deposit of the same
material in optical continuity.
Colonnes filtrantes, streams of
hot gases rising from the
Compose, heterogeneous, compo-
Cornes, hornfels, adinole and
allied products of contact
Corrosion, quartz de, see quartz
Couche, bed or stratum.
Coulee, lava stream or flow.
CulOt, plug (volcanic).
THE NOMENCLATURE OF PETROLOGY
Domaine, province (petrographi-
Ecoulement (structure d'), flow
or fluxion structure.
Eluviale, residual (deposits).
Enclaves enallogenes (Lacroix),
xenoliths or accidental inclu-
sions. (See page 90.)
Enclaves homceogenes (Lacroix),
autoliths or cognate inclusions.
Epanchement (Roches <2'), effu-
sive or volcanic rocks.
Epontes, walls of the country
rock enclosing a dyke or vein.
Exomorphisme, contact mctamor-
phism of the rocks invaded by
En coin, cuneMforme, wedge-
cross-- or current-bedded.
produced in a magma (and
hence in the resulting rock)
by interaction with the rocks
Entroques (calcaire a) , crinoidal
Epontes, walls of veins or dykes.
Faluns, shelly beds (Tertiary);
Farine fossile, diatom earth.
Fenestre~e (structure"], lattice
structure (e.g. of serpentine
after hornblende) .
Filon, vein, dyke.
Filon couche. sill.
Fluorine, fluor spar.
Galet, pebble, shingle.
Gemme, gem ; Sel genime = rock
Gisement, deposit; formation.
Gite metallifere, metalliferous
Glanduleuse (structure], augen
or phacoidal structure.
Grand, coarse sand; fine gravel.
Granitelle, a leucocratic quartz-
Granitite, a two mica granite, or
according to some authors a
plagioclase granite (adamel-
Granulite, muscovite-granite (cf.
English usage of term) .
Grenue (structure], granular,
granitic, saccharoidal ; a term
applied to holocrystalline rocks
in which there is no apparent
discontinuity in crystallisation.
Gries, detritus; intermediate in
grade between graviers and
Hemithrene, epidiorite rich in
phic. (See page 117.)
Houille grasse, bituminous coal.
Houille maigre, steam coal.
Houille seche, cannel coal.
Inclusions, term restricted to in-
clusions (gas, liquid, glass or
mineral) in minerals; not, as
in English, also denoting
xenoliths, etc. (cf. enclaves].
Labradorite, olivine-free basalt.
Laderes, sarsens (blocks of Eo-
cene sandstone which have re-
sisted denudation up to the pre-
Leptoclase, a minute fissure.
Libelles, gas inclusions in mine-
Lit, thin layer, lamina.
Lithoclase, rock fracture (of any
Maclifere, see Schiste macli-
Macline, spotted slate, chiastolite
Maillee (structure), mesh struc-
Menilite, nodules of opal.
Microgrenue (structure}. The
texture of a holocrystalline
rock with apparent discontinu-
ity in crystallisation (indicated
by the presence of pheno-
crysts) , the groundmass being
Microlitiique (structure}. The
texture of a porphyritic rock,
the groundmass of which is
composed largely of more or
less idiomorphic tabular or
prismatic crystals (e.g., felspar
laths) with or without inter
Minette, local name for the iron-
ores of Lorraine.
Miroirs de faille, slickensides.
Mortier (structure en~) , mortar
Nappe, sheet or flow (e.g., lava
flow or sill) .
Nu6e ardente, luminous cloud of
ash and gases (formed during
intense volcanic explosions of
CEilUJ (gneiss}, augen gneiss.
Ollaire (pierre), steatite; talc
OphioHte, a term for serpentine.
Paieovolcanique, term applied
to pre-Tertiary volcanic rocks.
Pdte vitreuse, glassy base.
Pendage or inclinaison, dip.
Phangrogene, coarsely granular
PoidS sp6cifique, specific gravity.
Quartz de Corrosion -.-
Quartz vermicule, drop-like in-
clusions of quartz in felspar;
intergrowths of quartz with
plagioclase, as in myrmekite.
2 4 6
THE NOMENCLATURE OF PETROLOGY
Recif corallien, coral reef
R6tiulee (structure], netted
structure (e.g., of serpentine).
Roches d'imbibition, rocks in-
jected by granitic magma e.g.,
Salse, mud volcano.
Schiste argileux, shale.
Schiste cristalin, schist.
Schiste maclifere, chiastolite
Sel gemme, rock salt.
Stade, stage or period (e.g., of
Synclase, contraction joints.
Tachete' (schiste) , spotted slate or
Terrains, formations, series of
Treillisee (structure] , lattice
structure (e.g., of serpentine,
Typhon, boss; stock; batholith.
Vermicu!6 (quartz), drop-like in-
clusions of quartz in felspars.
2 4 7
GERMAN PETROGRAPHIC TERMS
Compiled by Miss J. H. ROBERTSON
tion in a magma before crystal-
Abraumsalze, sulphates and
chlorides of potassium and '
magnesium (as in the Stassfurt
Absonderung, joint; parting (be-!
tween two beds of rock) ; j
cleavage or striation (e.g., of ;
diallage) ; separation or segre-
gation from a magma.
Abteilung, formation or series
Abyssische Spaltung, abyssal
Aohatmandel, agate amygdules.
Achsen, see Axen.
Adergneis, injected or vein-
Adlagnostisch, indistinguishable, j
Agjregatzustand, solid state.
Alteruptivgesteine, a general
designation for pre-tertiary
Angeschmolzen, fused, welded.
agents of weathering.
Aufgenommene Gemengteile, as-
Auflosungsgrenze, limit of
Ausfiillungsraume, infillings of a
Auskeilen, to thin out.
Ausjaugung, ilixiviation, leach-
Auslaugungshohle, cavities or
hollows due to solution or
Ausloschung, extinction (between
Ausscheiden, to separate out.
Austausch, exchange (e.g., of
material in alteration pro-
Auswurflinge, la-pilli, ejectamen-
Axenblld, interference-figure or
Eanderung, a streak, stripe or
THE NOMENCLATURE OF PETROLOGY
Begleitende Bestandmassen, as-
sociated constituents such as
concretions and secretions.
BildlOS, amorphous, structure-
Bildung, formation (of a rock).
Bildungsweise, mode of forma-
Biolithe, sediments of organic
Blaschen, gas bubble (in inclu-
Blatterstein, pillow-lava, vario-
lite, or spilite.
Blauschlamm, blue mud.
Bodenanalyse, soil analysis.
Bogenstruktur, see p. 48.
Bohnerz, pisolitic limonite.
Borsa'ure, boric acid.
Bruchig, clastic, fragmental.
Chemise he Verwandtschafts-
krafte, chemical affinity.
Daohschiefer, roofing slates.
Dampfsporen, gas inclusions.
Darg, peat formed from marine
Decke, sheet or cover (e.g., lava-
tion of density.
D i si ocat i o ns met a mor phi sm us ,
Doppelbrechung, double refrac-
Doppelgang, composite dyke.
Druck, pressure, compression.
Dunnschliff, thin section.
interpenetration, as in graphic
Edelsteinsande, gem sands.
EinSChlusse, inclusions, in either
minerals or rocks.
Eisener Hut, gossan.
Eisenoxyd, ferric oxide.
Eisenoxydul, ferrous oxide.
Endogene Einschlusse, cognate
inclusions, autoliths, enclaves
Entgasung, exudation of gas.
Erdharz, Erdpech, bitumen,
ErlanfelS, basic granulite.
Ersetzung, replacement, metaso-
Erstarrend, solidifying, crystal-
Erzader, mineral lode or vein.
Exogene Einschlusse, accidental
inclusions, xenoliths, enclaves
Explosionsrbhre, volcanic pipes.
Fahlbander, banded or foliated
rocks impregnated with sul-
Fallen der Schichten, dip of
Falsche Schieferung, false cleav-
age or bedding.
FHzartig, fllzlg, felted (applied
to felt-like aggregates of
minute elongated crystals) .
Fiaserig, "flaser"; lenticular
structure of dynamically meta-
Fleckschiefer, spotted slate.
FIBtz, seam, e.g., coal-seam.
Flugsand, blown sand.
Fluss Kieselsaure, fluo-silicic
Fluss-saurc, hydrofluoric acid.
Frittung, fritting, partial fusion
of country rock by volatile
Fruchtschiefer, knotted slate, in
which the spots vaguely resem-
ble ears of corn.
Gang, dyke, vein, or lode.
Ganggefolge, suite of related
series of dykes.
Ganggesteine, dike rocks.
Gangulmen, walls enclosing a
dyke or lode.
Gangwande, selvage of a dyke
Garbenschiefer, spotted slate or
schist, in which spots have a
Gebirgsbildende Prozesse, eroge-
Gebirgsdruck, orogenic pressure.
Gediegen, native (as applied to
Gekammerte Spheruliten, hollow
spherulites, or lithophysas.
Gelenkquarz, flexible sandstone.
Gemischte Gange, composite
Gepresster Granit, foliated
Gerblle, pebbles or boulders.
Gerichteter Druck, directed
Geschiebe, angular debris, scree
Gesteingase, magmatic gases.
Gesteinsserie, Brogger, 1894. A
series of related igneous rocks
possessing certain chemical,
mineral and textural features
in common, and exhibiting to-
gether a continuous variation
from one extremity of the
series to the other.
THE NOMENCLATURE OF PETROLOGY
Gestreckte, linear (applied to the
texture of foliated rocks) .
Gestrickte Formen, skeleton cry-
Gestrickte Struktur, netted struc-
ture (in serpentine formed
from augite) .
Gitterstruktur, lattice structure
(in serpentine, derived from
hornblende) ; cross hatching (in
Glasglanzend, of vitreous lustre.
Gle'-chmassig kornig, even
Gleichmassige Gesteine, rocks
of uniform grain.
Gleitflachen, gliding planes.
Granoblastische or Pflaster
Struktur, mosaic texture.
Griffelschiefer, pencil slate.
Griine Schiefer, chlorite schists
and allied metamorpliic rocks.
Grus, granitic sub-soil.
Halleflinta, a banded granulite,
having the composition of a
Hauptbruch, master joint.
Hauptgemengteile, essential or
Helizitische Struktur, helicitic
Herausgelost, dissolved or leach-
Hitzewirkung, action of heat.
Homooblastische Struktur, equi-
Hornstein, chert and allied sili-
Intrusivlage, intrusive sheet or
Injizierter Schiefer, injected
schists or gneisses.
Kalkabsatze, deposits of CaCO a ,
Karstenite, anhydrite rock.
Kaolinbildung, or Kaolinisle-
Keilartig or Keilfbrmig, wedge-
Kelyphitrinde, kelyphytic border.
Kies, coarse sand, fine gravel.
Kieselerde, siliceous earth.
Kieselguhr, diatomaceous earth.
Kieselsaure, silicic acid.
KieselStein, pebble, stone, flint.
Kieslagerstatten, pyritic deposits.
Klingstein or Klinkstein, phono-
Knotenschiefer, spotted shale
or slate (in the outer part of a
Kohlensaure, carbonic acid.
Kohlige Substanz, carbonaceous
Krummschieferig, sinuous or
Krystallgestalt, crystal form.
Krystallkern, nucleus of crystal-
Krystallskelette, skeleton cry-
Kugelgranit, orbicular granite.
Kugelige Absonderung, spheroi-
dal partings of igneous rocks.
Kugelige Verwitterung, spheroi-
Kuppe, puys, domes.
Lage, bed or sheet.
Langenschnitt, longitudinal sec-
Lepidoblastische or Schuppige
Struktur, flaky structure.
Lbcherig, pitted, porous, per-
Lockere Ablagerungen, loose
Magnet kies, pyrrhotite.
of limestone to marble.
Maschenstruktur, mesh structure
(in serpentine derived from oli-
Massenausbriiche, fissure erup-
Meeresabsatze, marine deposits.
Mikroscopieren, to examine
Mineraltrennung, separation of
Mischgesteine, migmatites, hy-
Mischkristalle, mixed crystals
(i.e., with isomorphous sub-
stances in solid solution) .
Monomineralisch, consisting of
but one mineral.
Mdrtelstruktur, mortar texture.
Murbrukstruktur, mortar tex-
Nachschube der Spaltungsges-
teine, subsequent intrusions of
differentiated rocks (comple-
Nadelchen, needle (acicular
Nebengemengteile, accessory or
Nematoblastische or faserige
Struktur, fibrous texture.
Neugebildet, secondary, authig-
OberflSchengesteine, volcanic, ex-
trusive, or effusive rocks.
Orientterter Druck, directed
THE NOMENCLATURE OF PETROLOGY
Pflasterstruktur, mosaic tex-
tion during powerful lateral
pressure (applied to the forma-
tion of the central granite of
Plattige Verwitterung, platy
weathering seen on the exposed
surface of certain igneous
Pleochroitische Hdfe, pleochroic
Poikiloblastische or helizitische
Struktur, helicitic texture.
pseudo-porphyritic texture (in
metamprphic rocks, due to the
presence of relatively large
crystals which have developed
in the rock by recrystallisa-
Putzen, xenoliths or cognate in-
Quadern, flags; term applied to
flaggy rocks and to those
which can be quarried in
blocks of cubic or rectangular
prismatic form ; freestone.
QuartZ-Keil, quartz wedge.
Quellkuppe, lava dome.
Querbruch, transverse fracture.
Quetschflache, crush plane.
Rand, edge, periphery.
Randfaoies, marginal facies (e.g.,
of an intrusion).
Rauchkalk, magnesian lime-
Reihenfolge der Kristallisation,
order of crystallisation.
Reihenfolge der Schmelzbarkeit,
order of fusibility.
Reisenkbrnig. very coarse
Roggenstein, oolite, roestone.
gliding planes in minerals.
Sahlband, selvage of a vein or
Salzsaure, hydrochloric acid.
Sanduhrstruktur, hour - glass
Saulige Absonderung, columnar
Schalige Abblatterung, spheroi-
SchaHge Verwitterung, spheroi-
SchalStein, sheared tuff, gener-
ally basic or calcareous.
Schicht, bed or layer.
Schichtflache, bedding or schis-
Schichtgestein, stratified rock.
Schichtung. bedding or strati-
Schieferung, cleavage (of rocks).
Schieferig, slaty, foliated,
Schiller, the shining lustre of
minerals such as hypersthene.
SchiiDerfels, serpentine contain-
Schizolithe, diaschistic or dif-
ferentiated dyke rocks.
Schlackenlava, scoriaceous lava.
Schlamm, mud, silt, ooze.
Schlammen, to elutriate.
Schlieren, streaks in igneous
rocks differing in texture and
composition from the normal
mass of the rock, but without
sharply marked boundaries.
Schmelzfluss, melt, or fused
Schmelzwarme, latent heat of
Schmelzpunkt, melting point.
Schmelzlosung, molten solution.
Schollenlava, block lava.
Schiippchen, scale of film.
Schwefelsaure, sulphuric acid.
Selfen, gem sands; placers.
SeitencJruck, lateral pressure.
Siebstruktur, sieve texture.
Sippe, tribe, series, e.g. " Atlan-
tic " and " Pacific " series.
Smirgel, or Schmergel, emery.
Sonderung, sorting out.
Spaltbarkeit, cleavage (of
Spezifisches Gewicht, specific
Spratzige Lava, Aa-lava.
" substitute " constituents
(e.g., sodalite in place of
Streckung, parallel or fluxion
structure (extension of
minerals along roughly paral-
lel lines due to flow or
Streichen der Schichten, stri! e
Strom, lava stream or flow.
Teig, paste, magma.
Teilmagma, partial or fractiona 1
THE NOMENCLATURE OF PETROLOGY
Ton, clay (often used in com-
bination \vith another noun,
or preceded by a specific adjec-
tive which gives the composi-
tion, e.g., Tonsckiefer = c\ay-
slate ; Kaolinisher Ton =
Transversals Schieferung, trans-
Trtimer, vein or dyke.
Trummergesteine, clastic rocks.
Tutenmergel, cone-in-cone struc-
types or members.
Ubergemengteile, secondary *
Umbildung, alteration, recon-
U mlagerung, rearrangement ;
paramorphism ; migration.
Ungeschlehtet, unstratified, mas-
Urgebirge, fundamental crystal-
Urschiefer, primeval schist.
Urspriinglich, original, primary.
Verkieselter Hornfels, silicified
Verschweiste Gange, welded
Vertikale Belastung, vertical
produced during action of
ducts of weathering.
Verzahnte Struktur, sutured
Wacke, weathering residue of
subsilicic igneous rocks.
Warmbrunnen, thermal springs.
Wesentliche Gemengteile, essen-
Wirkung (z.b. der Mineralbild-
ner), action (e.g. of minerali-
WUstensand, desert sand.
Zerkliiftung, fissure, joint.
Zersetzung, replacement of a
mineral by decomposition pro-
ducts other than those due to
Zonarer Aufbau, zonal structure
Zufuhrkanale, feeding channels.
Zugefuhrte Gemengtelle, sec-
ondary minerals (whose for-
mation involves the addition
of material from external
sources, e.g., tourmaline).
(mineral or chemical).
mesostasis (interstitial mat-
ABBREVIATIONS COMMONLY USED.
(an anderen Orten),
(am angefiihrten Orte),
in reference to, etc.
that is to say.
that is, i.e.
(und ahnliches mehr),
and the like.
(und andere mehr) ,
and others, and so on
(und so fort) ,
and so forth.
(und so weiter).
and so on, etc
(/urn Beispiel) .
for example, e.g
GREEK WORDS AND PREFIXES
a river in Sicily
God of the winds
a ray, spoke
I an almond
towards, up to
near at hand
first cause, origin
a test, means of
a bud, sprout
actinolite f stalactite,
allothi genous .
autoclastic, autoHth, auto-
THE NOMENCLATURE OF PETROLOGY
a bunch of grapes
a Greek letter (ch)
a crossing over
an old tree (e-g-,
EC, ex, exo
a choice selection (of
colours or min-
an adversary (to
to flow well
hospitable (rich in
a race, a kind
G rap no
hydr other mal, hydato-
under, nearly, less
down from, down
a rind, shell
crypto crystalline, crypto-
a scale, flake
THE NOMENCLATURE OF PETROLOGY
lithology; -tie (suffix in
rock and mineral
names) ; -ith (suffix in
terms such as batho-
lith, laccolith, denoting
mode of occurrence).
me gas co-pic.
anamesite, me socratic,
after (signifying a
met amor phi c, idiomcrphic.
my I o nit e.
old : palao-picrite.
-par agenesis, -paragneiss,
-p ar amor -phi c.
I show aphanitic, phenocryst,
of a reservoir
a stream, jet
to press together
-pi ezo crystallisation.
a felt -pilotaxitic, hyalopilitic.
a pea ! -pisolite.
a moulded image
the God of the I plutonic.
vapour ; pneumatolytic.
many -poly genetic, polymor-
purple, reddish \ -porphyry.
proto clastic, i>rotogir:e
-pyro clastic, -pyromeride,
THE NOMENCLATURE OF PETROLOGY
a plank, table
schist, aschistic, dia-
to look at
that which drops
to fall in drops
a meeting together
thermal, tlier mo dynamic.
a nibbler (e.g. trout)
smoke, a cloud
LATIN WORDS AND PREFIXES
ablation, abrasion, agglo-
to wash upon
calcrete, concrete, concre-
dedolomitisation , detritus.
to lay bare
to gather in a heap
to throw in
264 THE NOMENCLATURE OF PETROLOGY
a little stone
a small orb
o If vine.
a little time
to break back
Rocks and Ore-deposits 266
Igneous Rocks : *
1. Oversaturated : characterised by quartz 268
II. Saturated - 270
III. Undersaturated : characterised by olivine ... 272
IV. Undersaturated : characterised by felspathoids 274
V. Undersaturated : characterised by felspathoids
and olivine 276
Products due to Igneous Exudations ,. 278
Metamorphic Rocks . . 280
Exogenetic Rocks ... 282
Meteorites (Dr. G. T. Prior, F.R.S.) 284
* In these Tables the names of leucocratic rocks are printed in
italic, and those of melanocratic rocks in heavy type. See also
A. Johannsen : Journ. Geol., xxviii, 1920, p. 38, for a discussion
of classification and nomenclature that has appeared since the
pagination of this book.
2 66 THE NOMENCLATURE OF PETROLOGY
CLASSIFICATION OF ROCKS AND
I. ENDOGENETIC ROCKS and ORE-DEPOSITS.
Formed by processes of internal origin, which
processes operate deep-seatedly or from within out-
wards. High temperature effects constitute the
prevailing characteristic, and the water taking part
as an agent is partly of magmatic origin.
1. Igneous Rocks and Segregations.
2. Igneous Exudation Products.
(a) Contact impregnations and metasomatised
rocks, including pneumatolytic rocks and
(b) Hydrothermal vein rocks and deposits.
(c) Solfataric deposits.
3. Thermo -dynamically Altered Rocks and
* See T. Crook : Min. Mag., xvii, 1914, pp. 73-4 and 84.
APPENDIX E 267
II. EXOGENETIC ROCKS and ORE-DEPOSITS.
Formed by processes of external origin, which
processes operate superficially or from without in-
wards. These rocks are formed at ordinary or com-
paratively low temperatures, and the water taking
part in their formation is of atmospheric origin.
1. Weathering Residues.
2. Detrital Rocks (including Placer Deposits),
comprising- aeolian, alluvial, and marine sedi-
ments, loose or cemented.
3. Solution Deposits, loose or cemented.
(a) Surface Solution Deposits.
(i) Inorganic deposits,
(ii) Organic deposits.
(b) Percolating Solution Deposits.
(i) Certain vein deposits and cavity infill-
(ii) Metasomatic rocks and deposits, and
4. Accumulations of Organic Matter and their
THE NOMENCLATURE OF PETROLOGY
3 < Albite
natite. Graphic Gran
I Tsingtauite. Muscov
Kfe. Alsbachite. Bei
Granite. Granitite. <
oi <U "^
S oj ^
' 5 'C fl>
o -i CX
o .ti r, ii >
e. Grorudite. Paisan
E -S ^^
"^r 1 ? **
tJ C .0 a
- rf <a c3 -5
. --gQ e
3 "c3 X!
"S ~ tn
iS 3 H
' G >>
? XI OJ
I'S 'Ss ^
1|fl o| S
^i I'l "1,
2 1> ^ #
o c* o K -^
: ,0 D 4> T3 rt
' ? >! 'o N *V
si Is 1
rt ^ b O2 3
art ^ ^*o
THE NOMENCLATURE OF PETROLOGY
. 3 w .r"
"i ^"^ *
u> E ^
rt .0 =j
N "-' "o
S * <u
. Pulaskite. Ump
?" ~ ^
( ^ rf
"C -^ 2
*' *H d
O ( O
o ^ *
J2 c B
^ ^J .
*^ 3 J2 '
^ . *CU
cu l_ -2 0)
.1* 3 J
'* & S
sf^ 5 |
^'l ; l
OH ^ OJ
^ re +*
'<, *;?. i^aoraaonte Rock.
ro. Hyperite. Norite.
dite. Issite. Bojite. Corsite.
ite. Diabase. Ophite.
:e. Algovite. Vintlite.
rite. Alboranite. Nonesite
rgite. Variolite. Sudburite
3. Soggendalite. Arapahite.
//uft'/tf. Anorthite Rock.
e. Pyroxenolite. Diallagite.
. Hypersthenite. Websterite.
e. Ostraite. Rodingite.
5 ^Q re
!H .-. 03
^ -t-> Q ^ **
S - &
2 * "^ "
-J re Q
'5 'S -i
THE NOMENCLATURE OF PETROLOGY
o i o
.-, 0) O jj
G >v" G S
c -V oj J o
.1 .' ^
. 5J . &
IP i. i
iS^ 11 ^ 5
>'g^ 13 c
i*K s i i :
2 2* " ~ "
<= .22 -gflj 2
\&l !i 1 I
5^1 II 1
1 s I I
I'lSS .'=! >1 "E :
?.il\it li i
< (XaOSS3OO'B JO)
THE NOMENCLATURE OF PETROLOGY
CX 1 -22 a) ' -* rti
1 1 1 ll
i ' 1 ? ^ 2
c/) j - (3 jy s . y
+ : p O O '3
o 0) T3
J 3 <M
1 "| J M
^|j ^J ^ . QJ ^j
g a> . 'C 15 ^ -^ "5 'So -^
<u">, rt'"' : ''5 o
thoclase + Leucil
iwl^5 u 1.5
*t3 j <n^ Q? . '5.
co aj a> .ti '2 aj -^ 'E * - c5 '-2
o| .slJ si
ll 1 IflUlI 11
g, * <J C >. be 1 = tuo^
a> vJ - ^ < ^ 2 S c^
2 Q<< * H
1 a -
a 2 ^
-S . 8,S
<*-! S 3
,, WI V
1 H O
J l u
QJ - 3
*t5 *^n *^ ""^
<J ^s a 3
3 S -v
Hi ,i i 1 1
'i !. :ii i* I
.-Sl .SS -S"- ! 3.5,jS
| s -5 ffi-S^-n
1/5. 1 Srf , If,
% S H .Ss ^ ^ S a
^'H I 2|" a 1
I . s &c ^ I |
fc.3- 1 ^1 ^ S m
s ~ m Z c3
O _O Q
, ' (AJOSS90DB JO)
2 7 6
THE NOMENCLATURE OF PETROLOGY
: + Leuc
3 -Ms I
rt ; a
5 oJ Jj
.tr E g o5
jfl u |
1 1 5 |
OJ W (^
5 ^ *^
o 11 " |
278 THE NOMENCLATURE OF PETROLOGY
PRODUCTS DUE TO IGNEOUS EXUDATIONS.
of boron with a cer-
tain proportion of
Tro wleswor thite .
Do, with iron com-
pounds when associ-
ated with garnetisa-
Water and carbon
Silica, water, sul-
phides, and fluorine
Iron compounds, and
of chlorine, titanium
Hornblende - scapoli
ide, and sulphides.
ide, and potash-
Water, sulphides, and
Water, sulphates, and
Silica, water, sul-
| Water, carbon-diox-
i ide, sulphides.
Do, in solutions rich
in sodium and iron.
Zeolites, silica anc
Serpentinisation Water, sometimes
PRODUCTS DUE TO IGNEOUS EXUDATIONS.
Tourmaline - hornfels
and schist. Quartz-
Tourmaline - corun-
Various types of Gar-
-i Tertiary gold and f
(PRand gold <
(? Banket, in part).
Quartz-bary tes-rock .
V deposits. j
THE NOMENCLATURE OF PETROLOGY
2 2 .5*3
3? 8 S
5 rt i^J
s s B81
j ,-s *3 ^
3 S C -M
il 61- &
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THE NOMENCLATURE OF PETROLOGY
S' Talus 1
25 Boulders \
a; v. Gravel )
Later! tic Sand.
2 a Sand.
3 5 (Coral Sand.)
Adobe. Loess. | Loess.
Shale. 1 C. Shale.
s . Rock-flour.
Clay Rock. Argillite.
: (Coral Mud.)
Fireclay. Fuller's Earth.
5? ^ (Volcanic Mud )
^ (Red Clay.)
Calcareous, Dolomitic, etc.
Oolite. Pisolite. Pea Grit.
Coral ' Sands.' Coral Limestone.
Shell ' Sands.' Shelly Limestone
etc., etc., etc.
Lake and Be
>g Iron Ores,
THE NOMENCLATURE OF PETROLOGY
. o 5
<O & 13
. 6 6 ^
.s o o <u
- 1 ^r
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