updated 10/06

GeoMan's Mineral Identification Pages

LUSTER: Non-metallic

Streak Colorless or Light Colored

Hardness: < 2.5 (can be scratched with thumbnail)


Metallic | H<2.5 | H 2.5 to 3.5 | H 3.5 to 5.5 | H >5.5 | Glossary | Tests | Index

Rock Summary | Igneous | Sedimentary | Metamorphic

1 Good cleavage in 1 direction White, green, pink 2.7 Easily scratched with fingernail. Flexible but not elastic; foliated; slick or soapy feeling. Typical luster: pearly to waxy. Used on most baby's butts, and in paints, ceramics, rubber, insecticides, and paper. Variety SOAPSTONE can be carved into ornamental shapes and items. TALC
1-2 Fracture  White, tan, gray 2-3 Earthy; clayey odor. Earthy to dull luster. A swelling clay, used to stop leaks in soils, rocks, dams, and basement walls. Due to its excellent water-retention properties, it is also used as a soil additive and kitty litter. MONTMOR-


Uneven fracture

Yellow brown to red


Not truly a mineral (lacks a fixed chemical composition). Earthy to pisolitic (large round grains). Earthy, dull to waxy lusters. The most important ore of aluminum. BAUXITE
1-5.5 Conchoidal fracture Yellow, brown to black 2.7-4.3 Your basic rust. Many forms and lusters. Occurs as flattened crystals, massive, reniform, or stalactitic. Common secondary mineral in rocks and soils. An ore of iron. LIMONITE
1-6 Irregular fracture Brown, red, steel gray 4.8 to 5.3 Many forms and lusters (can also occur in metallic forms). Can be massive, radiating, botryoidal, and micaceous. The crystalline (metallic and sub-metallic) varieties are generally harder than the earthy (non-metallic) varieties. An ore of iron. HEMATITE


Conchoidal to uneven fracture



Characteristic bright yellow color; when small pieces are held in the hand close to the ear, crackling can be heard due to rapid, uneven thermal expansion. Pearly, waxy, resinous, to dull lusters. Used to make sulfuric acid, fertilizers, insecticides, explosives (kaBoom), and medicines. SULFUR


No macroscopic cleavage

 White, often colored by impurities


Earthy; clayey odor; absorbs moisture so rapidly that it will stick to the tongue. Earthy to dull lusters. Used in refractories, china, pottery and as a filler in paper. Also used in soft-serve ice cream to retard melting on hot summer days. KAOLINITE


1 direction, perfect, 2 directions, good

 Colorless, white, gray, gray-brown, pink reddish


As crystals and broad cleavage flakes with waxy to pearly to vitreous lusters (selenite variety); as compact fine-grained masses showing no visible cleavage, earthy to dull to waxy lusters (alabaster variety); as fibers with satiny luster (satin spar variety). Large crystals somewhat flexible, but not elastic. Used to make Plaster of Paris and sheetrock wallboard (drywall). GYPSUM


1 direction

Dark green to green-black


Thin sheets are flexible, but not elastic. Lusters typically resinous, waxy, vitreous, or dull. A common alteration mineral found in mafic igneous rocks (alteration of the ferromagnesian minerals to chlorite results in the greenish tint common to altered basalt, and the re-naming of the rock "greenstone").



Wavy, uneven fracture

Green and white


Platy or fibrous; waxy luster when massive, satiny luster when fibrous (asbestos variety). Used as an insulating material against heat and electricity. SERPENTINE
2.5 3 directions, perfect, cubic White when pure; may be red, blue, pink 2.1 to 2.3 In granular cleavable masses or cubic crystals. Soluble in water; salty taste. Typical lusters: vitreous, waxy, dull. Common salt: used as a source of sodium compounds and hydrochloric acid; used to salt highways in winter; used as a seasoning and preservative in food. HALITE


1 direction perfect

Pale brown, green, yellow


Common silicate mineral in felsic igneous rocks and low to medium grade metamorphic rocks. In foliated masses and scales. Transparent, flexible and elastic sheets. Vitreous to pearly luster. Used as insulating material in electrical appliances and as a fireproofing material. Also, Muscovite was used as windows before the invention of plate glass, was common as the rear window in early model convertible cars, and is still used as the front view-screen in many "fire-view" type wood stoves. MUSCOVITE MICA

2.5 to 3.0

1 direction, perfect

Dark brown, green to black


Common ferromagnesian silicate mineral in felsic to intermediate igneous rocks and low to medium grade metamorphic rocks. In irregular foliated masses and scales. Translucent, somewhat flexible and elastic sheets. Pearly to vitreous luster. Forms hexagonal crystals.



Metallic | H<2.5 | H 2.5 to 3.5 | H 3.5 to 5.5 | H >5.5 | Glossary | Tests | Index

Rock Summary | Igneous | Sedimentary | Metamorphic


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