Calcite, Fluorite, Sphalerite and Barite
Elmwood, Tennessee
This specimen measures 8cm x 15cm x 6cm
Flourite CaF2
Halide; Calcium fluoride, with small amounts of yttrium and cerium
Color and Luster: Violet, blue, green, yellow, brown, bluish black, pink, rose-red, colorless, white; vitreous; streak white
Hardness: 4
Cleavage: Perfect in four directions, forming and octahedron
Fracture: Uneven, brittle
Crystals: Isometeric; usually cubic or as penetration twins; less frequently octahedral and rarely dodecahedral; also cleavage masses, granular, columnar; penetration twins common
Barite BaSO4
Sulfates; Barium sulfate, often with small amounts of strontium
Color and Luster: White, gray, colorless, or shades of yellow, brown, red, blue; vitreous, pearly; streak white
Hardness: 3-3.5
Cleavage: Perfect in one direction, good in a second, and distinct in a third
Fracture: Uneven
Crystals: Orthorhombic; usually thin to thick tabular crystals; also prismatic crystals, divergent groups, compact, lamellar, fibrous, granular
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
Sphalerite ZnS
Sulfide; zinc sulfide, usually with some iron, manganese and cadmium
Color and Luster: Yellow, brown, red, green, black; rarely white or pale gray(Var. cleiophane); resinous, adamantine, submetallic; streak light brown (streak lighter than specimen)
Hardness: 3.5-4
Cleavage: Perfect in six directions
Fracture: Conchoidal; brittle
Crystals: Isometric; tetrahedral and dodecahedral forms common; faces often rounded; also cleavage masses, granular, compact, botryoidal
Note: Specimen donated by W. A. N. Severance
Photo by Mary Sutherland
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals