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Full text of "Tables for the Determination of the Common Minerals and Rocks"

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. ' • • 



Copyright 1914 
Copyright 1916 

by 

IV. A. TARR 






« 



INTRODUCTION 






A mineral may be defined as any inorganic substance found in nature 
that has a definite chemical composition. Minerals usually have ,a def- 
inite crystalline structure, also, but this is not essential, as is shown in 
the case of limonite, bauxite, and psilomelane. The tables include all 
the very common minerals and also a number that are less abundant, 
altho some of them may be very important as the source of some of 
the metals, such as galena, sphalerite, stibnite, hematite, etc. 

It is possible to determine the names of the various minerals by 
the use of their physical properties. The most important properties are 
streak, color, luster, hardness, cleavage, fracture, structure, specific gravity, 
and more rarely, odor, taste, feel, and magnetism. It Is always neces- 
sary to make these determinations upon a fresh specimen, because min- 
erals are changed by the action of water, gases, temperature, etc. But 
by using care, the minerals which are similar in some properties but dif- 
ferent in others, can be separated. 

The streak of a mineral is the color of its powder. This may be ob- 
tained by rubbing it upon a streak plate or by scratching or breaking up a 
fragment and noting the color. Fresh material must be used. The streak 
is the first property determined. 

The color of a mineral may always be the same, or it may range thru 
various shades of one color, or the >same mineral may have several different 
colors. 

Luster is defined as the appearance of the surface in reflected light. Min- 
erals are divided into two groups on the basis of their luster, viz., metallic 
and non-metallic. Minerals with a metallic luster reflect light like a metal. 
There are various lusters in the non-metallic group, common ones being 
vitreous, greasy, earthy, waxy, adamantine, resinous, etc. These are defined in 
the glossary. 

Hardness is the resistance a mineral offers to scratching. Use a good 

knife (a good knife blade usually has a hardness of about 5.5) or compare 

."^^ the mineral to another of known hardness. This is done by seeing which 

'^^ one in the known scale will scratch it. The common scale of hardness is as 

■ follows: 1 — talc, 2 — gypsum, 3 — calcite, 4 — fluorite, 5 — apatite, 6 — ortho- 

^ clase, 7— quartz, 8 — topaz, 9 — corundum, 10 — diamond. Fibrous or finely 

v^ granular minerals usually appear softer than the individual fibers or grains 

really are. Use the same pressure for all the minerals. In the group where 

the streak is white or light gray, the minerals are grouped according to their 

\ hardness. 

!t Cleavage is the property of minerals to break or split easily along certain 

"^ planes in the mineral. These planes are parallel to each other and are also 

:^ parallel to some possible crystal face. Thus a mineral with cubic cleavage 

* splits parallel to the cube faces, etc. There are various degrees of cleavage 

< which may be called perfect, imperfect, good, fair, or poor. 



/■ v» 



334S08 



Fracture Is that character of the surface obtained when a mineral is broken 
in any direction other than that parallel to the cleavage. There are several 
fractures as follows: conchoidal, uneven, splintery, hackly, smooth, and 
earthy. 

The various ways in which minerals can occur are known as structures. 
The great majority of minerals do not show crystal forms but occur in masses 
or aggregates. Various terms are in use to define these forms, the 
following being the most important; bladed, botryoldal, columnar, compact, 
crested, fibrous, foliated, lamellar, prismatic, nuimmillary, and stalactitic. 

The specific gravity of a mineral is its weight compared to that of an 
equal volume of water. This can be roughly determined by the use of the 
Jolly specific gravity balance, or on any balance. 

Some minerals have a distinct odor after they have been moistened or 
rubbed. Kaolin has an earthy odor after moistening by breathing upon it; 
pyrite gives off a sulfurous odor on being struck, etc. 

Those minerals which are soluble in water can be tasted. Salt or halite 
is a very common example of these. 

Various minerals feel smooth, soapy, clayey, or rough to the touch. 

A few minerals are attracted by a magnet, and one variety of magnetite 
acts as a lodestone or magnet itself. 

For further definitions see the glossary. 

Do not expect to find every property listed in the tables perfectly developed 
on each mineral. Such a case would be unusual, altho in most cases there 
will be a sufficient number of physical properties to determine the mineral 
easily. 

GLOSSARY 

Adamantine luster — like that of the diamo*nd. 

Basal cleavage — splits parallel to the end or base of a crystal. 

Bladed — elongated or flattened, like the blade of a knife. 

Botryoldal — closely united spherical masses, resembling a bunch of grapes. 

Cleavage — a property of minerals to break or split easily in certain directions, 

yielding approximately smooth surfaces. 
Columnar — long thick fibers. 
Compact — closely united. 
Conchoidal — the breaking of a mineral with a rounded or ^Curved surface like 

the Interior of a shell. ' . 

Concretion — rounded masses formed about a center. " i' 
Crested — flat, parallel crystals with their edges projecting as ridges. 
Crystal — XI — a substance bounded entirely or nearly so, by natural plane 

faces. 
Earthy — looks like clay, dull. 

Effervescence — the mineral dissolves, giving off a gas as bubbles. 
Fibrous — consists of slender fibers or threads. 
Foliated — in plates or leaves that separate easily. 
Fracture — any surface obtained when a mineral is broken not parallel to the 

cleavage. 
Hackly — rough surface covered with sharp points. 
Iridescence — usually a thin film on the surface of a mineral which produces a 

play of colors. 

(4) 



Lamella — small, thin plates or layers, curved or stral^-Iit. 

Luster — the manner in which a surface reflects light. 

Magnetic — attracted by a magnet. 

Metallic luster — reflecting light like a metal. 

Prismatic — a crystal elongated parallel to the vertical axis. 

Resinous luster — having the appearance of resin. 

Stalactites — cylindrical masses, resembling icicles. 

Rhombohedral — shaped like a rhomb. 

Sectile — capable of having slices cut off. 

Tarnish — a thin, colored film on the surface of a mineral. It differs from the 

color of the mineral. 
Vitreous luster — reflects light like glass. 
Waxy luster — reflects light like wax, or looks like wax. 
Xls — crystals. 

KEY TO THE TABLE 

1. streak Black or nearly so, to Steel Gray. 

Color: Dark Gray or Black. Page 6. 

Brass Yellow or Bronze to Purplish. Page 6. 

2. Streak Red or Brownish Red. Page 6-8. 

Color: Red or Brown. Page 7. 

Dark Gray or Black. Page 8. 

3. Streak Yellow or Yellowish Brown. 

Color: Yellow. Page 8. 

Brown or Black. Page 8. 
Yellowish Green. Page 10. 

4. Streak Blue or Green. 

Color: Blue or Green. Page 10. 

Dark Green or Black. Page 10. 

5. Streak Uncolored — White or Light Gray. 

Transmits light on thin edges. 

Hardness— 1-2.5. Can scratch with the finger nail. Page 10-12. 
Hardness— 2.5-5.5 or 6. Will not scratch glass. Pages 12-14. 
Hardness— 5.5 to 6 or over. Will scratch glass. Pages 14-18. 



(5) 



STREAK DARK GRAY TO BLACK 



H Color Streak Cleavage or Fracture Luster 

COLOR: DARK GRAY TO BLACK 



1-2.5 Steel gray to 
black 



Darker than Basal, perfect 
color 



Metallic 
dull 



2.2 



2 Dark lead gray Gray, black 

2.5 Dark lead gray Dark gray 

to black 

2.5-3 Dark lead gray Lead gray 



5-6 Grayish black; Brownish 
dull black to black 



Prismatic, gives Metallic 

long, shiny faces 



Cubic, perfect 



Metallic 



C — good but rarely Metallic 

seen 
F — conchoidal to 

uneven 



F — conchoidal 



4.5 



7.5 



5.5 
5.8 



Submetallic 2.2 
4.7 



5.5 Iron black 



Iron black 



F — uneven 



Metallic 



5.2 



COLOR: BRASS YELLOW TO BRONZE TO PURPLISH 

F — uneven Metallic 



3 Purplish, copper 3rayl8h 

brown, horse- black 
flesh brown. 

3.5 Deep brass yel- Greenish 

4 low black 



F — uneven to con- Metallic 
choidal 



4.9 
5.4 



4.2 



3.5 Bronze yellow Grayish 
4.5 Bronze brown black 



F — uneven 



Metallic 



4.6 



6 Pale brass yel- Greenish 
6.5 low black 



F — uneven 



Metallic 



6 Whitish brass 
yellow 



Black 



F — uneven 



Metallic 



4.U 



STREAK RED OR BROWNISH RED OR BROWN 

COLOR: RED OR BROWN 

F — earthy 



1.5 Reddish to 
3 brown 



Reddish 
bwn. 



Earthy, 
dull 



2.5 



1-4 Brownish red Dark red, 

to cherry red 'herry-red 



F — earthy 



Earthy, dull 

2.5-5 



2.5 Copper red 
3 



Copper red F — hackly 



Metallic 



8.8 



(6) 



STREAK DARK GRAY TO BLACK 



Structure 

COLOR : DARK 

Foliated, laminated, 
scaly, earthy 



Other Properties 

GRAY TO BLACK 



Name and Composition 



Prisms, often bent; 
bladed 

Cubes and granular 
masses 

Xls rare. Massive or 
as grains. 



Feels greasy; marks pa- 
per; sectile; scales flexi- 
ble, inelastic 

Brittle ; sometimes ir- 
idescent; tarnished 

Sectile to brittle; often 
found with sphalerite 

Often has a bluish tar- 
nish. Associated with 
pyrite, chalcopyrite, etc. 



Graphite, Carbon 

Stibnite, SbaSs 
Galena, PbS 
Chalcocite, CuS 



Massive rounded 
masses; kidney 
shaped 

Octahedrons, massive, 
granular to compact 



Tough to brittle; often 
found with limonite 



Psilomelane, MnOsH^O, 
etc. 



Brittle; strongly magnetic Magnetite, FcsO^ 



COLOR: BRASS YELLOW TO BRONZE TO PURPLISH 



Compact; massive 



Massive; compact; 
rarely in four-sided 
crystals 

Massive, granular 



Cubes, pyritohedrons, 
massive, granular 



Arrow shaped Xls, may 
have curved faces, 
stalactites 



Usually has many colors, 
but purple predomi- 
nates ; brittle 

Softer than pyrite, may 
have a tarnish; brittle 



Slightly magnetic; surface 
often tarnished bronze- 
brown 

Very common. Found ev- 
erywhere. Cubes are 
striated. Brittle 

Never in the form of 
cubes; white on fresh 
surface 



Bornlte, CusFeS* 



Chalcopyrite, CuFeS2 



Pyrrhotite, FctSs 



Pyrite, FeSj 



Marcasite, FeSj 



STREAK RED OR BROWNISH RED OR BROWN 

COLOR: RED OR BROWN 



Clay like masses with 
small round concre- 
tions 

Compact, granular, 
earthy, nodules, etc. 
Powder 

Hackly masses, sheets, 
wires, and crystals 



Distinguished from clay Bauxite, AljOs 2H2O 
by the concretions. 
Clayey odor 



Red ochre, looks like red 
clay, which it may be 



Malleable; often with a 
dark tarnish; sometimes 
greenish tarnish 



Hematite, FegOs 



Copper, Cu 



(7) 



STREAK RED, OR BROWNISH RED OR BROWN 
H Color Streak Cleavage or Fracture Luster 

COLOR: RED OR BROWN 



3.5 Brown, dark Reddish 

4 reddish bwn., bwn. 

red, deep red 



C — perfect. 12- sided Resinous, 
forms vitreous 



4.5 Red to reddish Pale reddish C — basal fair 
5 brown brown F — conchoidal 

uneven 



Vitreous, to 3.1 
to greasy 



COLOR: DARK GRAY OR BLACK 



2.5 Dark steel gray Brownish- 
6.5 to iron black red 



C — Micaceous 
(if present) 



Metallic, 4.4 

brilliant 5.3 



3.5 Brownish black Dark 
4 brown 



C — perfect. 12-sided Resinous, 4 
forms submetallic 



5-6 Dull black 


Very dark 
brown 


F — conchoidal 


Submetallic, 
dull 


3.7 
4.7 


6-7 Black 


Dark 
brown 


C — poor 


Submet. to 
metallic 


7 



STREAK YELLOW, YELLOWISH BROWN TO BROWNISH 

COLOR : YELLOW 



1.5 
2:5 


Sulphur yellow, 
honey yellow, 
straw yellow 


Pale 
yellow 


C — poor 

F — conchoidal 


Resinous, 
vitreous 


2 


1.5 
4 


Yellow 


Yellowish 
brown 


C— None 
F — earthy 


Earthy to 3.6 
dull. Silky 


3.5 

4 


Brownish yellow 
to yellow 


Pale 
yellow 


C— 12 sided, perfect 
F — uneven 


Resinous 


4 


COLOR: BROWN 


OR BLACK 








1.5 
3 


Brown or blfick 


Browns or 
yellow 


F — earthy 


Earthy to 
dull 


2.5 


1.5 

4 


Brown or black 


Brownish 
yellows 


F— earthy 


Earthy to 
dull 


3.6 


3.5 

4 


Brown to brown- 
ish black 


Brownish 
yellow 


C— 12 sided perfect 
F — uneven 


Resinous 


4 


3.5 
4 


Various shades 
of brown 


Pale yellow, 
ylw-brwn. 


C rhombohedral, 
perfect 


Vitreous 


3.8 


6-7 


Black, red- 
brown, yellow-' 
brown 


Pale ylw. 
gray-bwn., 


F — uneven 


Submetallic 


6.8 
7.1 



(8) 



STREAK RED, OR BROWNISH RED OR BROWN 

Name and Composition 



Structure 

COLOR: 



Other Properties 

RED OR BROWN 



Granular masses and Distinguished by its resi- 
crystals with round- nous luster, often with 

ed faces galena 



Sphalerite, ZnS 



Prismatic Xls usually. 
Massive, granular. 



Xls haye a fused appear- Apatite (CaF) Ca.^ 
ance. (POi)8 



COLOR: DARK GRAY TO BLACK 



Foliated, platy, 
micaceous, massive 
granular 

Massive, granular and 
in crystals 



Massive, granular, 
compact, kidney 
shaped 

Massive, as grains like 
sand, pebbles 



Bright sparkling plates or 
scales. Specular hema- 
tite 

May occur with galena, 
pyrite and chalcopyrite. 
See above 

Tough to brittle. Note dull 
luster and fracture 



Usually as grains and peb- 
bles. Very hard and 
heavy 



Hematite, Fe^Os 



Sphalerite, ZuS 



Psilomelane, MuOzHgO, 
etc. 



Cassiterite, SuOa 



STREAK YELLOW, YELLOWISH BROWN TO BROWNISH 

COLOR : YELLOW 



Massive, in crystals and Can be ignited with a 



as crusts 



Earthy masses and no- 
dules. Radiating 

Massive, cleavable mas- 
ses, crystals 



match and burns with a 
blue flame 

Yellow ochre. Looks like 
clay ; and often is clay 

Brittle. Often found with 
galena and chalcopyrite 



Sulfur, S 

Limonite, 2Fe2083H20 
Sphalerite, ZnS 



COLOR: BROWN OR BLACK 



Clay like masses con- 
tain concretions 

Massive, earthy 
Radiating nodules 

Massive, cleavable 
masses, crystals 

Rhombohedrons, 
cleavage masses, 
crystals 

Grains, pebbles with 
concentric structure 



Has a clay odor, often is 
hard. See above 



Bauxite, AI2O82H2O 



Brown ochre. See above Limonite, 2Fe20s3H20 



Very common color 



The cleavage or crystal 
faces are often curved. 
Brittle. 

Note the hardness and the 
gravity. Stream tin. - 



Sphalerite, ZnS 



Siderite, FeCOa 



Cassiterite, Sn02 



(9) 



STREAK YELLOW, YELLOWISH BROWN TO BROWNISH 



H Color Streak Cleavage & Fracture Luster G 

COLOR: YELLOWISH GREEN 

6-7 Yellowish green, Pale yellow C — basal, perfect Vitreous 3.3 

olive green, to white F — uneven 

nearly black 

STREAK BLUE OR GREEN 

COLOR: BLUE OR GREEN 



1-2 Dull green, 
often dark 



Greenish 
whitish 



F — earthy 



Dull 



2.2 



1.5 Grass green to Pale green 
2.5 dark green grylsh grn. 



C — basal, perfect 



Pearly, dull 2.8 
vitreous 



2-4 Bluish green to Pale green F — uneven to con- Vitreous, 2 

greenish blue Pale blue choidal earthy 2.3 



3.5 Bright green, Emerald 

4 dark green, green 

emerald green 



F — uneven, splintery Vitreous, 4 

silky, dull 



3.5 Azure blue 
4 

4-6 Light to dark 
green 

5-6 Blackish green 
to leek green 



Smalt blue 



F — uneven 



Sreenish wht. C — prismatic 
to white. 

3reeni8h-gray C — prismatic, 

pale green feet 



5-6 Dark shades of Sreenish gray 



green 



yellowish 



F — uneven 

C — prismatic, 

feet 
F — uneven 



COLOR : DARK GREEN TO BLACK 



per- 



per- 



5-6 Greenish black, 
pitch blk., 
brwn-black 

5-6 Greenish black, 
pitch-black, to 
brownish blk. 



Gray, green, 
brwn-gray 



Angle between the 
faces 124* 



reenish-gray C — Prismatic, good 



to gray 



angle between 
the faces SI" 



Vitreous, 3.8 
velvety 

Vitreous, 2.9 

silky 3.2 

Vitreous 3.2 

submet, 3.6 



Vitreous, 2.9 

silky 3.3 



Vitreous, 2.9 

silky 3.3 



Vitreous 3.2 

to dull 3.5 



STREAK UNCOLORED. WHITE OR LIGHT GRAY 

HARDNESS 1—2.6. CAN SCRATCH WITH FINGER NAIL 

White 



1 Green, white, 
1.5 gray 



1-2.5 Light to olive- White 
green, yellow- - . 
ish-green. 



C — basal, perfect 
F — uneven to splin- 
tery 



-fibrous 



Silky to 
greasy, 
silky 
metallic 

Pearly to 
greasy 



1-2.5 



2.6 

2.8 



(10) 



STREAK YELLOW, YELLOWISH BROWN TO BROWNISH 



Structure Other Properties 

COLOR: YELLOWISH GREEN 



Name and Composition 



Slender, striated 
prisms, massive, fi- 
brous, etc. 



Translucent to opaque. Epidote, Hydrous Ca, 

Has a peculiar green Al, Fe, silicate 

color 



STREAK BLUE OR GREEN 

COLOR: BLUE OR GREEN 



Grains or granular 
massives. Earthy. 



In foliated scaly, gran- 
ular, eartliy masses 



Massive, opal-like 
masses 



Fibrous, banded, sta- 
lactitic, botryoidal, 
masses 



Crystals, fibrous, 
banded, acicular 

Long slender crystals, 
radiating, fibrous 

Short, thick Xls., 8 
sided, granular 



Long slender Xls, fi- 
brous, blades, gran- 
lar 



Common in green sands. 
Also as grains in lime- 
stones and marls. 

Tough to brittle. Flexi- 
ble but not elastic like 
the micas. 

Brittle. Adheres to the 
tongue. Usually found 
with copper ores. 

Often as a stain on rocks. 
May be interlayered with 
azurite. Effervesces 
with HCl. 

Usually found with malac- 
hite. Like malachite. 

124' is the angle between 
the cleavage faces 

Distinguished from horn- 
blende by the 87* angle 
between faces 

Distinguished by its 6 
sided Xls and 124** angle 
between faces 



COLOR: DARK GREEN OR BLACK 



Long slender prisms, 
124** between cleav- 
age faces 

Short thick, 8 sided 
Xls. Angle 87" 



Common. Determined by 
the angle between faces 
as given above 

Brittle. Determined by its 
cleavage angle and 8 
sides 



Glauconite, 
Hydrous silicate 
of K and Fe. 

Chlorite, HgO, Mg, Al, 
silicate 



Chrysocolla, CuSiO« 
2H20 



Malachite, CuCOs 
Cu(OH), 



Azurite, 2CuCOs 
Cu(0H)2 

Actinolite, Ca(MgFe)8 

(SiO,)4 

Augite, Ca, Mg, Fe, Al, 
silicate 



Hornblende 

Ca, Mg, Fe, Al, 
silicate 



Hornblende, Ca, Mg, 
Fe, Al, SiOg 



Augite, Ca, Mg, Fe Al, 
silicate 



TRANSMIT LIGHT ON THIN EDGES 



Foliated, fibrous, com- 
pact masses 



Fibrous, rarely mas- 
sive 



Sectile. Greasy or soapy 
feel. Inelastic plates. 
Soapstone when finely 
granular 

Fibers flexible and easily 
separated. Feels smooth. 
Beautiful fibers. 



Talc, HgMgaSI^On 



Asbestos (chrysotile) 
H^MgsSiaOs 



(11) 



STREAK UNCOLORED OR WHITE OR LIGHT GRAY 
H Color Streak Cleavage & Fracture Luster G 

HARDNESS 1-2.5. CAN SCRATCH WITH FINGER NAIL 

1-2 Dull green, often White F— earthy Dull 2.2 

dark 



1-2.5 White, gray, White 

pink and red 



C — basal, perfect 
F — conchoidal 



Pearly, vltre- 2.2 
ous, silky 2.4 
dull 



1.5 Yellow 
2.5 



White 



F — uneven to con- 
choidal 



Vitreous to 2 
greasy 



1.5 White, yellow, 
2.5 brown, gray 



White 



F — earthy 



Earthy to 
dull 2.6 



1.5 Reddish, brown- 
3 ish, yellow, 

white 



White or the F — earthy 
same as 
color 



Earthy to 
dull 



2 White, gray. White 

2.5 yellow, brown 



C — perfect, into thin Pearly to 
sheets vitreous 



2.5 



2.7 
3 



2-2.5 Black, brown. White, gray, C— perfect, into thin Pearly to 2.7 
green sheets vitreous 3.1 



2-2.5 Dark to grass Gray, white, C— perfect, as very Pearly, vltre- 

green green fine scales ous, dull 2.8 



2.5 White, red, blue, White 
3 green, gray, 

etc. 

2.5 Light and dark White 
5 green, honey- 

yellow, white 

HARDNESS 2.5 to 6.6 or 6. 

2.5 White, red, blue. White 
3 green, gray, 

2.5 Light and dark White 

green, honey- 
5 yellow, white 

2.5 White, yellow- White 
3.5 isb, gray 

pinkish, brown 



C — cubic, perfect Vitreous 2.2 

F— Conchoidal 



F — uneven to con- Waxy, 2.5 

choidal, splintery greasy, dull 



WILL NOT STRATCH GLASS 

C — cubic, perfect Vitreous 

F — conchoidal 

F — uneven to con- 
choidal, splintery 



2.2 



Vaxy, greasy 2.5 
dull 



C — basal and pris- Vitreous, 
matic, good pearly 

F — uneven 



4.5 



White, pink 
yellow, red, 
brown, gray, 
green 



White 



C — perfect, cleaves Vitreous, 
into rhombohe- pearly, 
drons, even in dull 
very small frag- 
ments 



2.7 



(12) 



TRANSMIT LIGHT ON THIN EDGES 
Structure Other Properties Name and Compositioa 



Grains or granular 
massive. Earthy 



Tabular, transparent 
Xls, massive, granu- 
lar, fibrous 



Crystals, crusts, mas- 
sive 



Massive, compact 
masses, earthy, 
soapy, friable 

Massive with pea- 
shaped concretions 



In plates or books. 
Sometimes large. 
As scales 

In plates or books, 
scales, micaceous 



Micaceous scaly mass- 
es, lusterous 



Massive granular 
masses. Xls. 



Common in green sands. 
Also as grains in lime- 
stones and marls. 

3 varieties of gypsum. 
Cleaves into thin sheets 
not flexible or elastic — 
selenite. Fibrous — 
satin-spar. Granular 
massive — alabaster 

Brittle. Catches fire eas- 
ily and burns with a 
blue flame 

Clay odor when breathed 
upon. Adheres to the 
tongue. Plastic, greasy. 

Clay odor, distinguished 
from kaolin by the pea- 
shaped masses. 

Tough and transparent. 
Flexible and elastic. 
Splits easily. 

Tough. Dark colored even 
in the thinnest sheets. 
Splits easily. Flexible 
and elastic 

Tough to brittle. Flexi- 
ble, but not elastic like 
the micas 

Tough, Salty taste, solu- 
ble in water 



Glauconite, Hydrous- 
silicate of K and Fe. 



Gypsum, CaS042HcO 



Sulfur, S 



Kaolin, HAAlsSisOt 



Bauxite, AI2OS2H2O 



Muscovite, 

HsKAlsCSiOs)* 



Biotite, 
Silicate of 
H, K, Al, Mg, & Fe- 



Chlorite, HaCMg.Al 
Silicate 



Halite (Common Salt> 

NaCl 



Massive, compact, fi- 
brous 



Tough, brittle; smrooth, 
greasy feel 



WILL NOT SCRATCH GLASS 
Massive granular Brittle. Salty taste. Solu- 



masses. Xls. 

Massive, compact, 
fibrous 

Tabular, prismatic 
Xls. Crested or di- 
vergent groups. 
Compact, lamellar 



Long, sharp Xls and 
short Xls. Rhom- 
bohedrons, massive 
granular, cleavable 
masses. Found in 
cavities in many 
kinds of rocks 



ble in water 

Toii^h, brittle; smooth, 
greasy feel. 

Brittle. Easily determined 
by its high specific 
gravity and cleavage. 
Often found in lime- 
stones 

Perfect cleavage into 
rhombs, easy efferves- 
cence with hydrochloric 
acid make it easy to de- 
termine. Transparent to 
opaque. There are 
many varieties of caldte 



Serpentine. H4Mg8Si209. 



Halite (Common Salt)^ 

NaCl 



Barite (Heavy Spar) 

BaSO*. 



Calcite, CaCOg 



(13) 



STREAK UNCOLORED, WHITE OR LIGHT GRAY 
H Color Streak Cleavage & Fracture Luster 

HARDNESS— «. 6 to 6.5 or 6. WILL NOT SCRATCH GLASS 

White 



3-3.5 White, grayish, 
bluish-gray, 
gray, reddish 



C — perfect in two Vitreous 2.9-3 
directions, fair in to pearly 
the third 

F — uneven 



3.5 Gray, yellowish, White or 
brown, white, gray 
etc. 



C — good into rhom- Vitreous 

bohedrons with pearly 

slightly curved dull 
faces 



2.9 



3.5 Pink, gray, 
4 white, 

brown 



White to 
gray 



C — into rhombohe- Vitreous, 
drons pearly, 

F — conchoidal 



3.8 



3.5 Honey-yellow 
4 yellowish 

brown, red- 
dish 



White to 
yellowish 



C — perfect into " 12 Greasy, resi 3.9 

sided forms if nous 4.2 

complete. Not submetallic 
usual 



White, yellow, 
green, pink, 
purple 



White 



C — readily into oc- 
tahedrons or an 8 
sided forms 



Vitreous 



3 



3.5 White, gray, 
4.5 brown 



4.5 White to 
5.5 gray 



White 



White to 
gray 



C — rhombohedral 

perfect 
F — conchoidal 

when massive 

C — prismatic at an 
angle of 124". 



Dull to 3 
earthy, 

rarely 3.1 
vitreous 

Vitreous to 2.9 

silky 3.2 



4.5 Green, brown, Usually 
5 red, white, white 

gray, etc. 



C — basal fair • 
F — conchoidal — 
uneven 



Vitreous to 3.1 
greasy 



4-7 Blue, white, 
bluish gray, 
reddish and 
green 



White 



C— perfect in two Vitreous, 
directions produc- pearly 
ing bladed forms 

F — fibrous 



3.6 



HARDNESS Above 6.6 or 6. WILL SCRATCH GLASS 



5-6 Usually dark 

green or black 
but may be 
light green or 
white 



Lighter than 
the color 



C — has perfect 
cleavage giving 
an angle of 124* 

F — uneven 



Vitreous to 2.0 
silky 3.3 



5-6 Color usually Lighter than 

like the above the color 
mineral but 
lighter 



C — good, giving an Vitreous to 3.2 
angle of 87' dull bronzy 3.5 

F — uneven 



04) 



TRANSMIT LIGHT ON THIN EDGES 



Structure Other Properties Name and Composition 

WILL NOT SCRATCH GLASS 



Granular, massive, 
lamellar or fibrous 



Brittle. Looks like mar- 
ble or sugar. Not so 
heayy as barite. Acid 
has no effect. 



Anhydrite, CaSO^ 



Cleavable masses, Xls 
have curved faces 



Brittle. Nearly always 
some shnde of brown. 
Sp. (-r. Di88olves slowly 
in hot HCl. 



Siderite, FeCOj 



Usually has crystal 
faces which are 
curved. Granular 

masses. 



Has curved faces and does 
not effercesce in cold 
hydrochloric acid unless 
in a powder 



Dolomite, CaMg(COa), 



Granular, cleavable 
masses, Xls 



Resinous luster and good 
cleavage 



Sphalerite, ZiiS 



Very common as cubic 
Xls, granular; cleaves 
easily 



Massive, rarely 
crystalline. As dis- 
seminated grains 



Transparent to translu- 
cent. Easily determined 
by octahedral cleavage 
and hardness 

Conchoidal F, prominent 
nud characteristic. 



Fluorite, CaF, 



Magnesite, MgCOs 



Prismatic Xls, usually. Cleavage faces at an angle Actinolite, Ca(MgFe)» 
Massive, granular of 124* 



Bladed Xls, often 
radiating, fibrous 



Xls have a fused appear- Apatite, 
ance (CaF)Ca4(P04). 



As long blade-like 
Xls. 



Often has bluish spots in Cyanite, A^SIOb 
the Xls 



NOT SCRATCHED WITH A GOOD KNIFE AS A RULE 



Long, slender crystals. 
Bladed, fibrous, col- 
umnar 



May be softer, due to al- 
teration. Six sided 
crystals. Cleavage 
angles 124". Luster 
brighter than augite, 
cleavage also better 



Hornblende (several 
varieties). Silicate 
of Ca, Mg, Fe, Al 



Short thick Xls. Com- 
pact masses, etc. 



Recognized by the shape 
of the Xls. Cleavage 
faces at angle of 87". 
8 sided Xls. 



Augite. Silicate of Ca, 
Mg, Fe, Al 



(15) 



STREAK UNCOLORED. WHITE OR LIGHT GRAY 
H Color Streak Cleavage & Fracture Luster 

HARDNESS ABOVE 6.6 or 6. WILL SCRATCH GLASS. 



5-6 


White, light 


White 


C — perfect at an 


Vitreous 


2.9 




gray to light 




angle of 124" 


to silky 


3.1 




green, also 




F — uneven. 








pink 










5-6 


White to light 


White to 


C — good in two di- 


Vitreous 


3.2 




or rarely dark 


gray to 


rections at an 


often dull 


. 3.6 




green, gray- 


greenish 


angle of nearly 


rarely pearly 




ish 




90" 
F — uneven to 
conchoidal 






5-6 


Light to dark 


White to 


C — prismatic at an 


Vitreous to 


2.9 




green 


gray 


angle of 124** 


silky 


3.2 


4-7 


Blue, white, 


White 


C — perfect in two 


Vitreous, 


3.6 




bluish gray. 




directions produc- 


pearly 






reddish and 




ing bladed forms. 








green 




F — fibrous 






5.5-6 


White, gray, 


White 


C — poor 


Vitreous 


2.55 




greenish color- 




F — conchoidal 


to greasy 


2.65 




less 




to uneven 






5.5 


White, to 


White 


C — poor 


Vitreous to 


2.5 




gray 




B*— conchoidal 


greasy 




5.5 


Blue, gray 


White 


C— not distinct; if 


Vitreous 


2.14 


6 


white* green- 
ish, yellowish 




present, dode- 
cahedral 
F — conchoidal to 
uneven 


greasy 


2.30 


6 


White, pink, red. 


White 


C — perfect in two 


Vitreous, 


2.6 




yellow, green. 




directions at 90" 


pearly 






gray, black 




F — uneven, splintery 






6 


White, yellow- 


White 


C — good in two di- 


Vitreous, 


2.55 


6.5 


ish, green 




rections 
F — uneven 


pearly 




6 


Gray, often 


White - 


C— perfect in 2 di- 


Vitreous, 


2.7 




dark, grayish 




rections, nearly 


glassy 






white 




90» 
F — uneven 






6-6.5 


White, gray, 


White to 


C— perfect in 2 di- 


Vitreous, 






colorless 


white 


rections, nearly 
90* 
F — uneven 


pearly 
glassy 


2.6 


6-7 


Yellowish green, 


Grayish, 


C — basal, fair, not 


Vitreous, 


3.3 




dark green 


etc. 


common 
F — uneven 






6.5 


Various shades 


White 


F — uneven to sub- 


Vitreous, 


3.2 


7 


of green 




concholdal 


glassy 





6.5 Red, brown, yel- Usually 
7.5 low, pink, etc. colored 
black light 



F — uneven to con- 
choidal 



Vitreous, 3.4 

Rarely 4.3 

resinous 



(16) 



TRANSMIT LIGHT ON THIN EDGES 



Structure Other Properties Name and Composition 

NOT SCRATCHED WITH A GOOD KNIFE AS A RULE 

Tremolite, CaMgs(Si04)8 



Xls, usually long blad- 
ed or short and stout. 

In long thin Xls in ag- 
gregates, rarely fi- 
brous. 

Usually short thick 
prisms, nearly 
square or 8-sided, 
may be granular, 
rarely fibrous. 

Bladed Xls. often ra- 
diating, fibrous. 

As long blade-like 
Xls. 



Note good cleavage at 
124*, silky luster, and 
form of Xls 



Shape of Xls and cleav- 
age angles aid in its de- 
termination 



Cleavage faces at an angle 
of 124" 

Often has bluish spots in 
the Xls 



Diopside, . CaMg(SiOs)8 



Actinolite, Ca(MgFe)8 

(SiOs)4 

Cyanite, AUSiOs 



Usually massive or as 
embedded grains. 
Xls thick and 6- 
sided. 

Rounded grains, 
often with crystal 
faces. 

Xls are 12-sided 
forms. More com- 
monly massive or as 
grains. 



Xls, short 
Granular 
sive 



and thick, 
and mas- 



XI s fine. Cleavable to 
granular masses 

Large, cleavable mas- 
ses 



Cleavable masses. May 
show fine twinning 
lines on one face. 
Massive 

Long slender Xls, fi- 
brous. Massive. 
Xls may be striated 

Rounded green grains. 
Massive, granular 

Usually as crystals, 12 
to 24 sides. May be 
as rounded grains. 
Massive 



Note greasy luster and 
poor cleavage. Never 
with quartz, may be 
with sodalite, feldspar, 
etc. 

Brittle. In well develop- 
ed Xls or rounded 
grains in igneous rocks 

If blue, readily recogniz- 
ed, otherwise told by its 
associates, nephelite and 
leucite. Never with 
quartz 

Brittle. Two cleavages at 
about 90*. Commonly as- 
sociated with quartz in 
granite. Very common 
feldspar 

Only the green varieties 
can be distinguished 
from orthoclase 

Brittle. Often shows fine 
play of colors, greens, 
reds, blues, etc. Striated 
on one cleavage face 

Often twinned so as to 
show striations on the 
cleavage faces 

Recognized by its peculiar 
yellow green color. Very 
characteristic 

Brittle. Usually in basaltic 
rocks. Note its hard- 
ness and color 

Brittle. Opaque to trans- 
lucent. H. and color and 
shape aid in determin- 
ing it 



Nephelite, 

(NaK)AlSi04 



Leucite, 

KAl(Si08)2 

Sodalite, Na, Al, Sili- 
cate with some 
chlorire. 



Orthoclase, KAlSigOg 



MIcrocline, KAlSisOs 



Labradorlte, 
CaAlaSizOg 
and NaAlSisOs 

Alblte, NaAlSiaOs 



Epidote, 

Complex silicate of 
Ca, Mg, Fe, Al 

Olivine, (MgFe)2Si04 



Garnet, 
Silicate of 

Ca, Mg, Al, Fe 



(17) 



STREAK UNCOLORED. WHITE OR LIGHT GRAY 
H Color Streak Cleavage & Fracture Luster 

HARDNESS Above 7 WILL SCRATCH GLASS 



THE FOLLOWING ARE ALL VARIETIES OF QUARTZ. NO CLEAVAGE 
7 Colorless White 



F — coDchoidal to 
uneven 



Vitreous to 
greasy 2.6 



Pink 



White 



F — conchoidal to Vitreous to 

uneven greasy 2.6 



7 White and milky White 



F — conchoidal to Vitreous to 

uneven greasy 2.6 



Purple and White 

7 amethystine 



F — conchoidal to Vitreous to 

uneven greasy 2.6 



7 White, gray, 
etc. 



Banded, red, 
7 white, pink, 

brown, green, 
etc. 

7 Red, yellow, 
brown 



White 



White 



White 



F — marked con- Waxy to 

choidal to uneven vitreous, 2.6 

dull 

F — marked con- Dull to 

choidal to uneven waxy to 

vitreous 2.6 



F — m^irked con- 
choidal 



Dull, waxy 2.6 



7 Dark gray to White 
black 



F — marked con- 
choidal 



Dull, waxy 2.6 



7 White or light 
gray 



White 



F — marked con- 
choidal 



Dull, waxy 2.6 



fT r\„-i, ».««,,.« ♦-n. Non-colored 
7 Dark brown to ^ irravish 
nearly black ^^ grayisn 

7-7.5 Dark brown to White 
green, red, 
pink, etc. 

7.5-8 Green, yellow. White 
blue, pink, etc. 



C— fair in one di- 
rection 

C — not good 
F — uneven to sub- 
conchoidal 

F — conchoidal to 
uneven 



Sub-vitreous 
to dull or 3.65 
resinous 3.77 



Vitreous, 



Vitreous, 



4.4 
4.8 



2.6 

2.8 



9 Gray, bluish, 
brown and 
many other 
colors 



None 



C— fair in 3 or 4 di- 
rections 
F — conchoidal 



Vitreous to 3.9 
dull 4.1 



(18) 



TRANSMIT LIGHT ON THIN EDGES 
Structure Other Properties Name and Composition 

CANNOT BE SCRATCHED BY A KNIFE 



THE FOLLOWING ARE ALL VARIETIES OF QUARTZ. NO CLEAVAGE 



Usually as perfect six- 
sided crystals 



Usually as perfect six- 
sided crystals 
Also massive 

Massive and crystals 



Crystals, 6 sided. 
Massive 



Always massive 



Always massive and 
banded 



Massive and as 
nodules 



Massive and as 
nodules 



Massive and as 
nodules 



Brittle. No cleavage. 
Use hardness and luster 
(vitreous to greasy) and 
P. 

Brittle. No cleavage. Use 
hardness and luster 
(vitreous to greasy) 
and F. 

Brittle. No cleavage. Use 
hardness and luster 
(vitreous to greasy) and 
F. 

Brittle. No cleavage. Use 
hardness and luster 
(vitreous to greasy) and 
F. and color 

Tough. Determined by 
luster, fracture and 
toughness. Translu- 
cent 

Tough. Determined by 
luster, fracture and 
toughness. Translucent. 
Agate bands colored 

Tough. Determined by 
the luster, fracture, 
toughness and color. 
Opaque 

Tough. Determined by 
the luster, fracture, 
toughness and color. 
Opaque 

Tough. Determined by 
the luster, fracture, 
toughness and color. 
Opaque 



Rock Crystal, SiO« 



Rose Quartz, SiOa 



Milky Quartz, SlOj 



Amethyst, SiOi 



Chalcedony, Si'0» 



Agate and Onyx, SiO» 



Jasper, 



Flint. 



Chert, 



SiOt 



SiO» 



SiO» 



Prismatic Xls. 
Twins, 4. or X 
shaped 

Crystals, 6 sided or 
triangular in out- 
line 

Crystals, 6 sided, 
columnar 



Usually in short 6 
sided Xls. Barrel 
shaped 



Readily determined by 
hardness, flat Xls, and 
twins 

Brittle. Xls are striated 
vertically. Note tri- 
angular outline if in 
Xls 

Brittle. Translucent to 
transparent. Long Xls 
striated verticil ly. Very 
hard 

Tough to brittle. Easily 
determined by being 
harder than all other 
minerals 



Staurolite, 
Hydrous Fe Al si- 
licate 

Tourmaline, 
Very complex silicate 



Beryl, Be8Al2(SiO»)» 



CJotundum, AlsO«: 



. • 



(19) 



INTRODUCTION TO ROCK TABLE 

A rock may be defined as any material forming an essential part of 
the earth's crust. A rock is usually regarded as a hard substance and the 
term is generally applied to such materials, but it also embraces such soft 
materials as clay, mud, sand, etc. There are three great groups of rocks: 
igneous rocks, those that result from the solidification of molten material ; 
sedimentary rocks, those which are deposited by water, air, and ice; meta- 
morphic rocks, those produced from either of the first two by the various 
metamorphic processes which change the original materials either wholly or 
in part. The majority of the rocks found under the head of massive rocks 
in division III of the table are igneous rocks; divisions I and II contain the 
majority of the sedimentary rocks; while metamorphic rocks occur in all 
three of the major divisions. 

The following table is designed so that the student will use the physi- 
cal properties to separate the various kinds of rocks and thus lead up to 
the rock name. This has a tendency to prevent the use of pre-conceived 
ideas as to the name (which are only too often erroneous) and to cause 
the student to observe the real differences. 

It is only attempted to bring the more common rocks into the various 
divisions in such a way that they may be readily separated. In using the table 
first determine the hardness of the rock and this will rate it in division I 
or II or III. Care must be exercised in this determination altho the lines 
between the groups are not very close. Choose a fresh portion of the rock, 
especially if the surface is decayed and note whether the specimen is really 
scratched or whether some of the minerals are merely broken. In the case 
of the schists and gneisses the mica is apt to be merely scratched off the 
specimen. Having decided on which division it is in, it should be noted 
whether it is in group A (massive rocks) or group B (banded rocks). Under 
these groups the various rocks are arranged approximately according, to their 
hardness. This arrangement cannot be followed in Division III because the 
rocks are all very similar in hardness. Instead, the massive group, which is 
by far the largest group, is divided into sub-groups based on the size of 
the grains or 'minerals. The size of the grains and their relations to each 
other is what is known as texture. Once a specimen is located in a group 
the application of the specific tests given will soon separate the various rocks 
and give the proper name. 

The tables do not attempt to bring together the rocks which belong to 
the same petrographic class. The primary object is to get a name for and 
learn something about the composition and physical properties of the rock. 

The materials of the sandstones and conglomerates are usually cemented 
together or consolidated by pressure. The cements may be calcium carbonate 
(calcite), silica, clay, or the iron oxides, usually hematite, but also limonite. 
It should be noted that shales often are calcareous or they may contain some 
sand and sometimes considerable of the iron oxides. Limestones often contain 
clay or sand and this should be noted. 

Note.— Acetic acid can be used in testing for calcium carbonate, but not 
for dolomite. Use hydrochloric acid for the latter. When using hydro- 
chloric acid do not put more than a small drop on the rock, always putting 
It on a fresh surface. 



GLOSSARY 

Massive — uniform in color and size of grains iu all directions. 

Banded — shows line^ or bands of different color or different mineral com- 
position, or l>^(Jaing planes. 

Foliated— in bands which are more or less curved. 

(20) 



Porphyry — a rock which contains some crystals that are larjrer than the 
remainder, although the latter may be large enough to determine. The 
larger crystals are called PHENOCRYSTS. When the phenocryst is de- 
terminable its name may be used as a partial name for the rock, thus, 
if hornblende were the phenocryst, the rock name would be hornblende 
granite, or hornblende felsite, etc. 

(iroundmass — the fine-grained part of the rock in which the phenocrysts are 
embedded. 

KEY TO TABLE 

I. The specimen can be scratched with the finger nail. 
Hardness less than 2.5 or 3.. 

A. Massive. Pages 21-22. 

B. Banded. Page 22. 

II. Rocks that cannot be scratched with the finger nail, but can be scratched 
with a knife blade. A good knife has a hardness of about 5.5.' 

A. Massive. Pages 22-23. 

B. Banded. Page 23. 

III. All rocks that are harder than a knife blade. 

A. Massive (1) 

1. Grained rocks. The grains over 1-16 of an inch, or determ- 

inable. Pages 23-24. 

2. Fine-grained rocks. The grains less than 1-16 of an inch, 

Pages 24-25. 

3. Glassy rocks. Page 25. 

B. Banded rocks. Page 25. 

(1) Most of the rocks in this group may be porphyritic, that is, they 
may contain some mineral or minerals larger than those in the ground 
mass. 

I. ROCKS THAT CAN BE SCRATCHED WITH THE FINGER NAIL. 
A. MASSIVE. 

1. Soft, friable, earthy masses, usually white, yellow, or gray. 
Effervesces with cold hydrochloric acid. CHALK. If it has 
a clayey odor when breathed upon and sticks to the tongue it is 
called MARL. 

2. Soft, crumbly, clayey odor, sticks to tongue, sticky and plastic 
when wet, smooth, greasy feel when rubbed for sometime between 
the fingers. White, gray, yellowish, and various other colors. 
Breaks irregularly. CLAY. 

3. White to gray, crumbly, no odor, not plastic, does not effer- 
vesce. DIATOMACEOUS EARTH. 

4. White, yellow, red, grained masses. No odor, no effervesence. 
Sometimes fibrous or may be in transparent plates. GYPSUM. 

5. Similar to 2, but harder and has compact, dull appearance. May 
effervesce. Breaks into chips. SHALE. (See B-2.) 

6. Grained; white, red, gray, blue; has salty taste — soluble in water. 
ROCK SALT. 

7. Friable, crumbles easily, not scratched. Colors : white, red, 
brown, green, yellow, etc. Grains merely broken apart and not 
scratched, composed of rounded or angular grains of quartz and 
sometimes feldspar. May effervesce. SANDSTONE. (See ll-A-6 
and 7.) 

(21) 



8. Soft; white, gray; no odor usually, but may have; composed of 
Tarious sized angular materials, such as broken minerals, rocks, 
pumice, etc. Porous and light, usually. TUFF. 

9. White, sharp, brittle, very porous, the openings are often very 
large; crushed with the nail. Does not effervesce. SILICEOUS 
SINTER. 

10. Gray or green of various shades, often dark, the light colored ones 
often showing a shining surface; shows no cleavage; has smooth 
to gritty feel; and consists of talc, some chlorite, and other ma- 
terials. SOAPSTONE. 

B. BANDED ROCKS. Show bedding planes or are foliated. 

1. Dense; gray, white, blue, yellow, and other colors: may be 
finely laminated, otherwise like 2 (above). CLAY. 

2. A dense rock, may be coarsely or finely laminated, otherwise like 
A— 5 (above). SHALE. 

3. Greenish; greasy feeling in foliated masses; easily cleaves Into 
leaves that bend but do not spring back. The leaves may be small 
and may be mixed with other minerals. TALC-SCHIST. 

4. Green to dark green, very fine grained, dense, smooth feel, shining 
luster, may have crystals of other minerals. CHLORITE- 
SCHIST. 

5. Very friable and crumbles easily in the fingers. Banded. SAND- 
STONE. (See A— 7) 

6. Banded; composed mainly of mica; shiny luster on two sides of 
the rock; thin layers. Black, white, gray, brown, and green. 
Rarely so soft. MICA-SCHIST. (See II— B-6) 

II. ROCKS HARDER THAN FINGER NAIL AND SCRAltjHED WITH 
KNIFE. 

A. MASSIVE. Do not show bands or bedding planes. 

1. Has salty taste. (See I— A— 6) ROCK SALT. 

2. Dense, dull in appearance, clayey odor. Shell like fracture. Same 
as I— A— 5. SHALE. 

3. White, gray, pink, yellow, etc.; grained. No effervescence or odor. 
(See I— A— 4) GYPSUM. 

4. Dense to granular; shell-like to smooth fracture; usually easily 
scratched with knife, H — 3; color: white, blue, gray, black, red, 
etc. Effervesces briskly with cold hydrochloric acid, may contain 
fossils. LIMESTONE. 

When impure may have clayey odor; then called argillaceous 
limestone; when grained it is called MARBLE. 

6. Similar to the above, except harder, about 4; heavier, and does not 
effervesce with cold acid unless in fine powder. Will effervesce 
along a scratch. May be porous. DOLOMITE. 

6. Porous, brittle, does not effervesce. (See I — ^A— 9) 

SILICEOUS SINTER. 

7. Grains rounded or angular, more or less cemented, with cal- 
otte, iron, clay, or silica; may effervesce; may crumble; grains 
mainly of quartz. Color white, red, brown, gray, etc. SAND- 
STONE. Same as I— A— 7. 

(22) 



8. Similnr to 6, only contains feldspar and mica. ARKOSE. 

9. Composed of rounded pieces of rocks and minerals more or lesf 
firmly cemented together with clay, calcareous material, or even 
fine sand. Colors vary, usually depending on materials of same; 
grays, brown, reds, etc. The materials are larger than peas. May 
effervesce. CONGLOMERATE. 

Sometimes the fragments are angular, it is then called a BRECCIA. 

10. Angular pieces of various igneous rocks and minerals in more or 
less fine, ash-like material. Color: white, gray. May look like a 
felsite. Rarely has clayey odor. TUFF. 

11. Yellowish green, dull to waxy luster, dense, smooth to splintery 
fracture. Hardness 2.5 — 5 may be harder if quartz is present. 
Smooth to greasy feel. SERPENTINE and SERPENTINE ROCK. 

B. BANDED ROCKS OF ABOVE HARDNESS. Several of the above 
rocks show some kind of banding. 

1. Dull, dense, splits off in chips, shell like fracture, banded, clayey 
odor, no effervescence. SHALE. (See I — A— 5) 

2. Effervesces easily with acid. H— 3. See 3 above. The bands may 
be very fine. LIMESTONE. 

3. Effervesces only along scratch, harder and heavier than 2. See 4 
above— DOLOMITE. 

4. Composed of grains of quartz, see 6 above. The bauds may 
be due to different colors or mineral grains. SANDSTONE. Com- 
posed of grains of feldspar or mica, ARKOSE. See 7. 

5. Dense; dull to shiny luster cleaves into thin plates which ring 
when struck; splintery fracture on the ends; gray, black, green, 
red, etc. SLATE. 

As the mica becomes larger and more abundant the slate becomes 
PHYLLITE. 

8. Contains much mica, some quartz also, cleaves irregularly. Color 
black, gray, white. The scales of mica peel off easily. May contain 
crystals of garnet, or other minerals. No feldspar. MICA SCHIST. 

7. Very dark green, usually black, shiny luster, minerals generally 
long and fibrous. Hardly scratched with knife. Has ap- 
pearance of a mass of needles. HORNBLENDE SCHIST. 

III. ROCKS WHICH CANNOT BE SCRATCHED WITH A KNIFE BLADE 
OR CAN BE SCRATCHED WITH DIFFICULTY. 

A. MASSIVE ROCKS. 

1. GRAINED, THE GRAINS OR MINERALS EASILY DISTIN- 
GUISHED, OVER 1-16 INCH. 

(a) Composed of feldspar and quartz, with or without other min- 
erals. Color: white, gray, pink, red, or green. GRANITE. 
There are the following varieties: 

1. Quartz, feldspar, and biotite. BIOTITE GRANITE, also 
called TRUE GRANITE. 

2. Quartz, feldspar, muscovite, and biotite. MUSCOVITE— BI- 
OTITE GRANITE. 

3. Very coarse-grained granite, crystals one inch or more in 
size. PEGMATITE. 

4. Medium-grained granite witli large porphyrltlc crystals. 
PORPHYRITIC GRANITE, 

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5. Fine-grained granite with phenocrysts, or a dense rock com- 
posed of more than 50% of quartz and feldspar as pheno- 
crysts. GRANITE PORPHYRY. 

6. Quartz, feldspar, mica, and hornblende or tourmaline, etc. 
The Inst gives the roclc its name, as HORNBLENDE 
GRANITE, TOURMALINE GRANITE, etc. 

(b) Composed of feldspar with little or no quartz. Color: white, 
gray, , shades of red. SYENITE. 

1. Contains feldspar and nephelite. NEPHELITE SYENITE. 

2. Contains dark feldspar, which may show twinning lines, or 
a play of colors, as blues, reds, greens, etc. The rock is 
usually dark gray. ANORTHOSITE. 

3. Contains feldspar, hornblende, or mica. HORNBLENDE or 
MICA SYENITE. 

4. Fine-grained syenite with phenocrysts, or a dense rock with 
more than 50% of feldspar as phenocrysts. SYENITE 
PORPHYRY. 

(c) Rocks composed of hornblende and feldspar, or some mica. Color 
usually light gray. Heavy. DIORITES. 

1. May be called MICA DIORITE if mica is abundant. 

3. Fine-grained with phenocrysts. DIORITE PORPHYRY. 

(d) Composed of a pyroxene and feldspar (usually dark). Color: 
usually very dark. Heavy. GABBRO. 

1. Composed of feldspar, pyroxene, and olivine. OLIVINE 
GABBRO. 

2. Composed of feldspar, pyroxene, and mica. MICA GAB- 
BRO. 

3. Large crystals in dark, crystalline groundmass. GABBRO 
PORPHYRY. Not common. 

(e) Composed of less than 50% of feldspar and some undeterminable 
ferromagnesian mineral. DOLERITE. 

1. Phenocrysts of feldspar, hornblende^ or pyroxene in a 
groundmass of feldspar and some undeterminable fer- 
romagnesian mineral. DOLERITE PORPYYRY. 

(f) (1) Composed of pyroxene and olivine. PERIDOTITE. 

(2) Composed of pyroxene. PYROXENITE. 

(3) Composed of hornblende. HORNBLENDITB. 

(g) This group is more or less light colored, usually some shade of 
gray, green, or black. 

1. Epidote and quartz or some feldspar. EPIDOTE ROCK. 

2. Garnet and either ferromagnesian minerals or possibly 
feldspar and quartz. GARNET ROCK. 

(h) Very hard and tough; minerals; all quartz; vitreous to dull luster; 
rounded grains may be seen cemented together; breaks through 
the quartz grains and not around them as in sandstone; may be 
banded. QUARTZITE. 

2. FINE-GRAINED, DENSE ROCKS, THE MINERALS LESS THAN 
1-16 INCH AND NOT RECOGNIZABLE. If a porphyry, the 
phenocrysts must make up less than 50% of the rock. 

(a) Light colored rocks; white, red, brown, yellow, light gray, and 
light green. Break with more or less splintery edges. FELSITB. 

1. Same but with phenocrysts (less than 50% of rock) set in a 
dense groundmass. The phenocrysts may be of any mineral 
and may give the name to the rock. FELSITE-PORPHYRY 
or LEUCOPHYRE. 
May also say QUARTZ-FELSITB-POBPHYRY, etc, 

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(b) Dark colored rocks; dark gray, dark green, black. BASALT. 
May be porous aud slaggy looking. Holes are rounded or elongat- 
ed. Scoriaceous Jt>asalt. 

1. Same with phenocrysts (often olivine). BASALT-POR- 
PHYRY. 

(c) Like (h) above— QUARTZITE. 

(d) Dense, dark gray to nearly black, tougb, has splintery to con- 
choidal fracture. HORNSTONE. 

3. ROCKS COMPOSED WHOLLY OR IN PART OP GLASS. 

1. Black, red, brownish, greenish, vitreous, conchoidal fracture. 
OBSIDIAN. 

2. Resinous, oily or greasy luster, dull, fracture less shell-like 
than obsidian, generally light colored. PITCHSTONE. 

3. A glassy rock full of tubular openings, usually white, and 
very light and porous. Often has a satiny luster. Brittle. 

PUMICE. 

4. Either 1 or 2 naay contain phenocrysts ; then called a VITRO- 
PHYRE or OBSIDIAN-PORPHYRY. 

B. BANDED OR FOLIATED ROCKS. These rocks may sometimes 
be very much crumpled and folded. 

1. Composed of mica with some quartz, garnets, and other 
minerals. Mica may be biotite or muscovite. The mica can 
be scratched easily. Colors vary widely. Very shiny on the 
cleavage faces. Layers usually thin. MICA-SCHIST. 

2. Similar to above but with excess quartz, 50% or more. 
QUARTZ-MICA-SCHIST. 

3. Dark rock; greenish to black; consisting of long, slender 
crystals of hornblende. Often has fibrous appearance or 
radiating appearance on the surface. Bands not readily 
seen. HORNBLENDE-SCHIST 

4. Banded rock; gneissic or foliated; usually rather coarse 
bands; white, red, gray, green, as rule light in color; com- 
posed of feldspar with several minerals. Several varieties 
are known. GNEISS. 

Thus if it has the mineral composition of a granite it is 
called granite-gneiss; of a syenite, syenite- gneiss, etc. Or, 
it may contain garp^ts, then called GARNET-GNEISS, etc. 



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INDEX OF MINERALS 



Actinolite 11, 15, 17 

Agate 19 

Alabaster 13 

Alblte 17 

Amethyst 19 

Anhydrite 15 

Apatite 9, 15 

Asbestos 11 

Augite 11, 15 

Azuvite 11 

Barite 13 

Bauxite 7, 9, 13 

Beryl 19 

Biotite 13 

Bornite 7 

Calcite 13 

Casserite 9 

Chalcedony 19 

Chalcocite 7 

Chalcopyrite 7 

Chert 19 

Chlorite 11, 13 

Chrysocolla 11 

Chrysotile 11 

Copper 7 

Corundum 19 

Cyanite 15, 17 

Diopside 17 

Dolomite 15 

Epidote 11, 17 

Flint 19 

Fluorite 15 

Galena ^ 7 

Garnet 17 

Glauconite 11, 13 

Graphite : 7 

(•ypsum 13 



Halite 13 

Hematite 7, 9 

Hornblende 11, 15 

Jasper 19 

Kaolin 13 

Labradorite 17 

Leucite 17 

Limonite 9 

Magnesite _^ 15 

Magnetite 7 

Malachite 11 

Marcasite ^ 7 

Microcline 17 

Milky Quartz 19 

Muscovite 13 

Nephelite ± 17 

Olivine 17 

Onyx 19 

Orthoclase 17 

Psilomielane 7, 9 

Pyrite 7 

Pyrrhotite 7 

Quartz 19 

Rock Crystal 19 

Rose Quartz 19 

Satin-spar 13 

Selenite 13 

Serpentine 13 

Siderite 9, 15 

Sodalite 17 

Sphalerite 9, 15 

Staurolite 19 

Stibnite 7 

Sulfur 9, 13 

Talc 11 

Tourmaline , 19 

Tremolite 17