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Laboratory Manual for Introductory Geology 4e

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APPENDIX 3.1

Mineral Identification Flowcharts

B. Minerals with Nonmetallic Luster, Dark Colored

Hardness Breakage Color

Other diagnostic

properties

Possible minerals

(see Appendix 3.3 for

additional properties)

Softer than

a penny

Perfect cleavage

in one direction;

splits into thin

sheets

Dark brown,

black, greenish

gray or

brown, green

Elastic cleavage sheets; transparent

Flexible cleavage sheets; opaque

Biotite

Chlorite

Conchoidal or

irregular fracture

Bright yellow

Yellow streak; greasy luster

Sulfur

Six directions;

not all visible at

once

Brown, black,

dark reddish

brown

Resinous luster;

pale yellow streak

Sphalerite

Three directions

not at 90°

Light brown

Looks like calcite but doesn’t

react with hydrochloric acid

Siderite

Harder than

a penny,

softer than

glass

Usually too

fine grained

to tell

Red,

reddish brown

Yellow-brown

Green, often

banded

Earthy luster; reddish brown

Earthy luster; yellow-brown

Reacts with hydrochloric acid

Hematite

Limonite

Malachite

Deep blue

Reacts with hydrochloric acid

Azurite

About the

same as

glass

Cleavage in two

directions

at 87° and 93°

Cleavage in two

directions

at 56° and 124°

Dark green or

brown

Dark green or

brown

Commonly in elongate crystals

Commonly in elongate or

needle-like crystals

Pyroxene family

(commonly augite)

Amphibole family

(commonly

hornblende

or actinolite)

Harder

than glass

Cleavage in two

directions

at 90°

Cleavage in two

directions not

at 90°

Conchoidal

fracture

White, gray,

black

White, gray,

pink, green

Brown,

reddish brown

Striations on one cleavage

direction; may be iridescent

No striations; may have narrow,

ribbon-like exsolution lamellae

Often in stubby crystals; may occur

as cross-shaped pairs of crystals

Plagioclase

feldspar

Potassium

feldspar

Staurolite

Very variable Often in elongate 6-sided crystals Quartz

Red, green

Green

Often in equant 12-sided crystals

May occur in granular masses

Garnet

Olivine

Rarely seen Apple green Often granular or powdery coating

Epidote

76 CHAPTER 3 MINERALS

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