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 |
| 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 the 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. A common ferromagnesian mineral in mafic to ultramafic silicate rocks. | PYROXENE GROUP |
| 6.0 |
2 directions, good at 90° |
Colorless, white, pink, red, gray, green, blue |
2.5 to 2.6 |
As cleavable masses or irregular grains in rocks; as crystals in pegmatites and some igneous bodies. Luster generally vitreous to pearly. Used in manufacture of some porcelains. Orthoclase is the common feldspar found in felsic silicate rocks. Common varieties include MICROCLINE (pink), and AMAZONITE (blue). | ORTHOCLASE FELDSPAR GROUP |
| 6.0 |
2 directions, good at 86° |
Colorless, white, gray to black |
2.6 to 2.8 |
In cleavable masses or irregular grains. Striations common on cleavage planes. Luster generally vitreous to pearly. Used in manufacture of some ceramics. Forms a continuous series from the calcium rich variety to the sodium-rich variety (refer to Bowen's Reaction Series). Plagioclase is the common feldspar found in intermediate to mafic silicate rocks. | PLAGIOCLASE FELDSPAR GROUP |
| 6.5 |
Uneven fracture |
Red to brown |
4.3 |
Usually in 12 or 24 sided crystals (commonly as porphyroblasts in schists): also massive. No cleavage, but some samples may exhibit parting. Typical lusters: resinous, vitreous, dull. Used as an abrasive: well formed crystals may be used as gemstones. | GARNET |
| 6.5 to 7.0 |
Conchoidal fracture |
Olive green to yellow green |
3.3 to 3.4 |
Usually as disseminated grains in mafic igneous rocks; as granular masses having saccharoidal texture (looks like grains of sugar). Luster generally vitreous. Mined for refractory sand used in casting industry. A common ferromagnesian mineral in mafic to ultramafic silicate rocks. | OLIVINE |
| 7.0 |
Conchoidal fracture |
Colorless or white when pure, but may be any color |
2.6 |
As crystals with hexagonal cross section, often with striations on prism faces. Also as crystalline masses, granular aggregates, irregular grains, etc. Luster generally vitreous to greasy. Varieties include MILKY (white to cloudy, usually due to included microscopic air bubbles); SMOKEY (gray to black); ROSE (pink); AMETHYST (violet). Used as a gemstone, to make glass, as a source of silicon for the computer industry, a flux, a filler, and an abrasive. | QUARTZ |
| 7.0 |
Conchoidal fracture |
Various colors |
2.6 |
Translucent to opaque. Varieties include AGATE (massive to banded, many colors); FLINT (dark gray to blue); CHERT (light-colored, white to gray); JASPER (commonly red but can include many hues); OPAL (milk-white, yellow, green, red, multi hued with "fire," waxy luster); CHALCEDONY (brown to gray, fibrous to botryoidal). Agate and opal are used as gemstones. | MICRO- |
| 7.0 to 7.5 |
Cleavage not prominent |
Varied; black common |
3.2 |
Usually in trigonal prismatic crystals with prominent lengthwise-running striations. Typical lusters: vitreous to dull. Well-formed and colored crystals used as gemstones. Commonly occur in prgmatite dikes, and in higher grade metamorphic rocks. | TOURMALINE |
| 7.0 to 7.5 |
Cleavage not prominent |
Red-brown to brownish-black |
3.7 |
Cruciform twin crystals common; also elongate bladed crystals with rhombic cross sections. Luster resinous to vitreous when unaltered; dull to earthy when altered or impure. Well-formed, cross-shaped twins used in jewelry ("Fairy Crosses"). | STAUROLITE |
| 8.0 |
Imperfect cleavage |
Green to yellow |
2.7 |
Hexagonal, prismatic crystals. Luster generally vitreous. Used as a source of beryllium for metal alloys. High quality crystals used as gemstomes. | BERYL |
| 8.0 |
1 direction, poor |
Colorless, pink, yellow |
3.5 |
Prismatic crystals, crystalline or granular masses. Luster generally vitreous. High quality crystals used as gemstone. | TOPAZ |
| 9.0 |
Parting, no true cleavage |
Brown, pink, ruby-red |
4.0 |
Crystals generally hexagonal prisms, commonly barrel-shaped. Basal parting common. Typical lusters: vitreous to dull. Used as an abrasive; high quality, colored crystals used as gemstones: RUBY (red), SAPPHIRE (blue). | CORUNDUM |
| 10 |
4 directions |
Colorless, pale yellow |
3.5 |
Uncut crystals have a characteristic greasy appearance; well-formed crystals are octahedral. Luster: adamantine. Industrial diamonds (borts) used as abrasives; high quality diamonds used as gemstones. | DIAMOND |
| 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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