updated 10/06

GeoMan's Mineral Identification

LUSTER: Non-metallic

Streak Colorless or Light Colored

Hardness: 2.5 to 3.5 (cannot be scratched with thumbnail; will not scratch penny)


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


1-5.5 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
2-3 Wavy, uneven fracture Green and white 2.5 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.


2.5 to 3.0

3 directions, perfect @75°

Clear, translucent, dark brown, green to black


Crystals in many forms. Occurs as large granular masses (limestone and marble) and fine granular or fibrous masses in which the cleavage is not prominent; also compact masses. Effervesces in cold, dilute HCl. Typical lusters: vitreous, pearly, waxy. Used in manufacture of cement, crushed stone, and as agricultural lime.


3 to 3.5

1 direction, perfect, 2 directions, good

White or gray


Crystals usually tabular or bladed. Barite's distinctive characteristic is its specific gravity, which is very high for a nonmetallic mineral. Typical lusters: vitreous, pearly to dull. Used in powder form to give weight to drilling muds in order to prevent "blow-outs" of oil and gas wells, and to maintain the stability of the hole in diamond core and rotary drilling.



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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