Earth Minerals

MAGNETITIE

An oxide of iron (Fe3O4). Magnetic, back color, metallic luster, black streak, hardness 6, specific gravity 5.18, is an ore of iron.

FLUORITE

Calcium Fluoride (CaF2). Vitreous luster, octahedral cleavage, often in cubic crystals, hardness 4, specific gravity 3.18, transparent to translucent, variable colors, used as a flux and as a source of fluoride for oral hygiene and the production of hydrofluoric acid.

CALCITE

Calcium carbonate (CaCO3). Usually white to colorless, rhombic cleavage, vitreous to earthy luster, crystals transparent to translucent, may show double refraction (Iceland Spar), hardness 3, specific gravity 2.72, reacts strongly to hydrochloric acid, source of lime for use in soil treatment and manufacture of cement and mortar

DOLOMITE

Calcium magnesium carbonate (Ca Mg[CO3]2). Usually pinkish but may be white, brown, or other colors, hardness 3.5-4, specific gravity 2.85, less vigorous reaction with hydrochloric acid, vitreous to pearly luster, source of lime for soil treatment.

GYPSUM (SELENITE)

Hydrous calcium sulfate (CaSO42H2O). Usually white or colorless, vitreous luster, transparent to translucent, tabular crystal form, soft with hardness of 2, specific gravity 2.32, three unequal cleavages, may show fibrous fracture, used in dry wall and plaster, used for fertilizer.

TALC

Hydrous magnesium silicate (Mg3Si4O10[OH]2). Very soft with a hardness of 1, greasy or soapy feerl, pearly to greasy luster, micaceous habit, usually greenish to white in color, powdered form used as a filler in paint, paper, and rubber, etc., used for talcum powder and in ceramics.

Galena

Lead sulfide (PbS). Commonly found in cubic crystals, cubic cleavage, lead grey color, metallic luster, grey streak, hardness 2.5, high specific gravity (7.4-7.6), ore of lead.

OLIVINE

Magnesium iron silicate ([Mg,Fe]2SiO4). Olive to grayish or yellowish green color, vitreous luster, transparent to translucent, conchoidal fracture, granular texture, hardness 6.5-7, specific gravity 3.27-3.37, not of any real economic importance.

BAUXITE

Mixture of aluminum hydroxides. Dull to earthy luster, hardness 1-3, typically pisolitic (round pea-sized grains), may be claylike, specific gravity 2-2.55, ore of aluminum.

SPHALERITE

Zinc sulfide (ZnS). Dodecahedral cleavage, yellowish brown to brown color, typically resinous luster, typically yellow streak, hardness 3.5-4, specific gravity 3.9-4.1, powder treated with warm hydrochloric acid produces rotten egg smell, is the ore of zinc.

HORNSBLEND

A complex hydrous silicate containing aluminum, calcium, magnesium, sodium, and titanium. Vitreous to silky luster, dark green to black color, prismatic cleavage, hardness 5-6, specific gravity 3.2, common rock-forming mineral, no economic importance.

GARNET (ALMANDITE)

A complex silicate containing aluminum, calcium, chromium, iron, and magnesium in various combinations. Vitreous to resinous luster, commonly dodecahedral crystal form, commonly reddish in color, hardness 6.5-7.5, specific gravity 3.5-4.3, used as a gem stone and for abrasives.

AUGITE

A complex silicate containing calcium, magnesium, iron, aluminum, is various combinations. May have good prismatic cleavage, cleavage angle of almost 90° distinguishes it from hornblende, green to dark black in color, vitreous luster, hardness 5-6, specific gravity 3.2-3.4, common rock-forming mineral, no economic importance.

KAOLINITE

A hydrous aluminum silicate (Al2Si2O5[OH]4). Soft with hardness of 2-2.5, usually dull luster, usually claylike masses, looks earth, feels chalky, specific gravity 2.6-2.63, used to make fine china and ceramics, used as a filler in paper r and paint

MICA (MUSCOVITE)

A hydrous potassium aluminum silicate (KAl3Si3O10[OH]2). Usually a light brownish color, basal cleavage permitting it to be split into thin sheets which are very flexible and elastic, vitreous luster, transparent to translucent, hardness 2-2.5, specific gravity 2.76-3.1, used for electrical insulators, heat insulation, windows in stoves, etc.

HEMATITE

Iron III oxide (Fe2O3). Granular form dark grey to black in color, earthy forms rust red, granular metallic luster, earthy varieties dull luster, reddish streak, hardness 5.5-6.5, specific gravity 5.26, most important ore of iron.

PYRITE

Iron sulfide (FeS2). Bright yellow color, metallic luster, greenish black streak, commonly in cubic crystals, hardness 6-6.5, specific gravity 5.02, ore of iron and source of sulfur for making sulfuric acid. Called "Fools Gold" because of its color and luster.

FELDSPAR (ORTHOCLASE)

Potassium aluminum silicate (KAlSi3O8). Vitreous luster, white to reddish color, hardness 6, specific gravity 2.57, prismatic cleavage which forms angle of 90 degrees. The feldspars a)re the most common rock-forming minerals of Earth's continental crust. Used to make porcelain and other

QUARTZ

Silicon dioxide (SiO2). Conchoidal fracture, hexagonal crystal form, vitreous luster, transparent to translucent, hardness 7, specific gravity 2.65, usually colorless or white but impurities often color it, no cleavage. Second most abundant rock-forming mineral of Earth's continental crust. Used as an abrasive, in glass manufacturing, in electronics. Some forms are used as semiprecious gems (amethyst, citrine, opal, etc.).

HALITE

Sodium chloride (NaCl). White or colorless, cubic cleavage, vitreous luster, transparent to translucent, salty taste, hardness 2.5, specific gravity 2.16, used for table salt and source of chlorine for chemicals.