Celestite
Agrigento, Sicily
This specimen measures 8cm x 5cm
Celestite SrSO4
Sulfate; strontium sulfate, sometimes with much barium
Color and Luster: White, colorless, bluish, reddish; vitreous, pearly; streak white
Hardness: 3-3.5
Cleavage: Perfect in one direction, good in a second, and distinct in a third
Fracture: Uneven, brittle
Crystals: Orthorhombic; usually thin to thick tabular crystals; also fibrous, cleavage masses, nodular; rarely granular or lamellar
Photo by Mary Sutherland
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals