updated 10/06
| Metallic | H<2.5 | H 2.5 to 3.5 | H 3.5 to 5.5 | H >5.5 | Glossary | Tests | Index |
| HARD | BREAKAGE PATTERN |
COLOR | SP. GR. |
REMARKS | NAME |
| 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 |
| 3.5 to 4.0 | 3 directions, perfect at 75° | White, pink, brown, gray, etc. | 2.9 | Usually harder than a penny. As crystals with curved faces (twisted rhombs), and as granular masses (dolostone, dolomitic marble). Effervesces in cold, dilute HCl only if powdered. Typical lusters: vitreous, pearly, waxy. Used as a building and decorative stone. | DOLOMITE |
| 3.5 to 4.0 |
Perfect cleavage in 6 directions |
Yellow to brown, black, reddish brown |
4 |
Usually massive. All six cleavages rarely seen on a single specimen. Luster typically resinous, but may be adamantine on well developed crystals. The most important ore of zinc. | SPHALERITE |
| 3.5 to 4.0 |
3 directions, perfect, rhombic |
Light to dark brown; maroon |
4 |
As crystals with curved faces; usually cleavable; sometimes in granular masses. Effervesces in dilute HCl only if powdered. Typical lusters: vitreous, pearly, waxy. A minor ore of iron. | SIDERITE |
| 4.0 |
Good in 4 directions, octahedral |
Purple, green to yellow, colorless |
3.2 |
Well-formed cubic crystals, and also massive. Typical lusters: vitreous, pearly. Used in production of hydrofluoric acid, and as a flux in steel making. The fluorine used in fluoridation of public drinking water supplies and toothpastes comes from fluorite. | FLUORITE |
| 5.0 |
Poor cleavage, 1 direction |
Green to brown |
3.2 |
Massive and granular. Vitreous luster when i large crystals; earthy luster when in fine-grained earthy masses. High quality crystals are used as semiprecious gemstones. Most important use is as source of phosphate for fertilizers. | APATITE |
| 5.0 to 6.0 |
2 directions, good, at approx. 60° and 120° |
Black to green |
3.0 to 3.3 |
Crystals slender, fibrous. Often look like long, skinny rods. Commonly occur in cleavage fragments or granular masses. Typical lusters; vitreous to dull. HORNBLENDE is a common ferromagnesian mineral in intermediate silicate rocks (granitic to dioritic composition). | AMPHIBOLE GROUP |
| 5.0 to 7.0 |
Good in 1 direction |
Blue to green |
3.6 |
In bladed aggregates. Cleavage parallel to length of crystals. Hardness variable. Typical lusters: vitreous, pearly, dull. Used in manufacture of spark plugs and other high refractory porcelains. | KYANITE |
| 5.5 to 6.0 |
2 directions, poor to fair, at approx. 90° |
Green to black |
3.1 to 3.5 |
Crystals "stubby" with nearly rectangular cross section. Commonly in granular or crystalline masses. Typical lusters: vitreous to dull. Common ferromagnesian mineral in mafic to ultramafic silicate rocks. | PYROXENE GROUP |
| Metallic | H<2.5 | H 2.5 to 3.5 | H 3.5 to 5.5 | H >5.5 | Glossary | Tests | Index |
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