Mineral Dichotomous Key

Luster

Hardness

Cleavage/ Fracture

Streak Color

Mineral Color

Unique Properties

Test updated

Specific Gravity or density

Mineral Name

Metallic

Soft

Excellent

Black

Black, Silver, Gray

Leave black marks, opaque, slippery, sometimes cleavage is not apparent

2.23

Graphite

Dark Gray

Silvery gray, tarnishes dull gray

Opaque, Perfect cubic cleavage in three directions at right angles, about 2.5 hardness, Soft to medium in hardness

7.4 to 7.6

Galena

No Cleavage

Greenish black, black

Brassy Yellow

Opaque, Brittle

4.1-4.3

Chalcopyrite

Medium

Excellent

Gray to white, colorless

Dark gray, green, black

Cleavage at intersecting angles of 60 and 120 degree, can be considered nonmetallic, opaque, tabular crystals or in mass. Hardness at about 5.5, brittle, splintery

3.0-3.3

Hornblende

No Cleavage

Reddish

Reddish brown, black, silver

Opaque, Sometimes magnetic, Sometimes oolitic

5.56

Hematite

Black

Black or silver

Opaque, magnetic

5.18

Magnetite

Hard

Brassy Yellow, Looks like gold

Conchoidal fracturing, opaque, sometimes has cubic crystals,

5.02 hefty

Pyrite

Nonmetallic

Soft

No Cleavage

white

White, gray, yellow, red, brown, orange

Dull and earthy luster, translucent, opaque, pisolitic

2.7-4.3

Bauxite

Yellow

Yellow

Yellow crystals or earthy masses, greasy to resinous luster, may have a strong odor, flammable

2.0-2.1

Sulfur

Poor

White

White, gray, yellow, beige, brown, orange, reddish brown

Found in compact masses, crystals are rarely visible, brittle, opaque, once in awhile translucent, cleavage can be found, but rare

2.6

Kaolinite

Green, gray, white, silver, other colors

Cleavage is usually indistinct, pearly, greasy, opaque, translucent, tiny flakes when rubbed, very soft, powders

2.7-2.8

Talc

Excellent

White

White, gray, green, yellow, clear

Perfect cleavage in three directions, rhombic, vitreous, pearly, effervescent, double refraction

2.71

Calcite

Colorless

Dark green, dark brown, black

Cleavage in one direction breaking off in thin sheets, translucent, flexible, bendable

2.8-3.2

Biotite Mica

Clear, white, yellowish, silvery

Vitreous, pearly, transparent, excellent cleavage in one direction, breaks off into thin sheets,

2.7-3.0

Muscovite Mica

White

White, gray, blue, red, clear

Excellent cleavage in 3 sides at 90° angles, tastes salty, vitreous, pearly, transparent, translucent, dissolves in water,

2.16

Halite

White, gray, brown, red,

Vitreous or pearly luster, transparent, translucent, sometimes as fibrous masses

2.3-2.4

Gypsum

Medium

Excellent

Colorless

Brown, dark green, black

Cleavage at intersecting angles of 60 and 120 degree, can be considered nonmetallic, opaque, tabular crystals or in mass. Hardness at about 5.5, brittle, splintery, can be vitreous.

3-3.4

Hornblende

White

Pink, white, gray, others

Cleavage in 3 direction, rhombic, vitreous, pearly, translucent, transparent, effervesces if powdered

2.85

Dolomite

Any color, mostly clear, yellow, purple, blue

Perfect in 4 directions, vitreous, translucent, transparent, sometimes fluorescent

3.18

Fluorite

Poor

white

Green, brown, yellow, pink, violet

Poor cleavage in one direction, vitreous, transparent, translucent, brittle, fractured masses

3.1-3.2

Apatite

No Cleavage

reddish

Red-brown, silver, black

Dull luster, opaque, sometimes oolitic, sometimes magnetic

5.26

Hematite

Hard

Excellent

White, colorless

White, gray, pink, clear, green, yellow

Vitreous, transparent, translucent, cleavage at 90° angles, few striations if any

2.5-2.6

Orthoclase/ Potassium Feldspar

White, gray, clear, blue, green

Vitreous, transparent, translucent, striations on cleavage faces

2.6-2.8

Plagioclase Feldspar

No Cleavage

Colorless

Olive, green, brown

Conchoidal fracturing, vitreous, transparent, translucent, usually granular masses

3.27-4.27

Olivine

Any color

Conchoidal fracturing, vitreous, greasy, transparent, translucent, can have hexagonal crystals

2.65

Quartz

White

Gray, blue, red, brown

Transparent, opaque, or translucent might see hexagonal prisms with striated flat ends,

3.9-4.1

Corundum