Dark-Colored Minerals

Minerals with a dark color are generally relatively rich in the elements iron (Fe) and magnesium (Mg). Colors for these minerals include gray, black, brown (including "gold") and dark green, and these minerals will often leave a good streak. The dark-colored minerals listed below are among the most common rock-forming minerals, and are listed in order of decreasing hardness (from hardest at the top to softest at the bottom of the list).

		OLIVINE(Mg,Fe)2SiO4 - Hardness=7 (harder than glass), generally no obvious cleavage, density 3.3-4.2 g/cc, olive green color, sometimes occurs in sandy masses. Olivine is a silicate mineral.
		MAGNETITE (Fe3O4) - Hardness=6, no obvious cleavage, density 5.2 g/cc, dark gray to black (dark gray streak), strongly magnetic (use the small end of the magnet to test). Magnetite is an oxide mineral.
		AUGITE (a mineral in the PYROXENE family) - Hardness=5-6, two cleavages at approximately 90 degree angles, density 3.2-3.5 g/cc, commonly dark green to black; one of the more common dark-colored minerals in igneous rocks. The pyroxene minerals are silicates
		HORNBLENDE (a mineral in the AMPHIBOLE family) - Hardness=5.5, two cleavage directions at 60/120 degree angles, density 3.0-3.3 g/cc, commonly dark green to black (doesn't leave much of a streak); one of the more common dark-colored minerals in igneous rocks. The amphibole minerals are silicates.
		HEMATITE (Fe2O3) - Hardness=5-6.5, no obvious cleavage, density 4.9-5.3 g/cc, silver (specular hematite) to gray or reddish brown (reddish brown streak), may be weakly magnetic; this is "rust" (or oxidized iron) and is a common coloring agent for sedimentary rocks. Hematite is an oxide mineral.
		BIOTITE (K(Mg,Fe)3(Al,Fe)Si3O10(OH)2) - Hardness=2.5-3, one perfect cleavage direction (peels off in thin sheets - one of the mica minerals), density 2.7-3.1 g/cc, dark brown to black. The micas are members of the silicate group.

Light Minerals

Common Minerals

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