Calcite
Smith Quarry
Black Rock, Arkansas

The largest crystal measures 12cm by 6cm


Calcite      CaCO3

Carbonate; calcium carbonate

Color and Luster: White, colorless, pale shades of gray, yellow, red, green, blue, brown to black when impure; vitreous, dull; streak white

Hardness: 3

Cleavage: Perfect in 3 directions, forming a rhombohedron

Fracture: Conchoidal, seldom observed

Crystals: Hexagonal; crystals commonly showing a rhombohedron, scalenohedron, and prism; also tabular, acicular, cleavable, granular, compact, stalactitic, oolitic, earthy; twinned crystals very common

Photo by Mary Sutherland


Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals