Calcite
Rio Grande do Sul, Brazil
The calcite "flower" specimen shown here measures 9cm x 11cm x 13cm, and was crystallized within a gas pocket trapped by lava flows in the state of Rio Grande do Sul, Brazil. It was acquired for the collection from Hawthorneden in 1995.
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
Calcite is the most common and widely occurring species of the carbonate mineral class. It belongs to the hexagonal - rhombohedral crystal system, and has been found in more than 700 different crystal forms(habits).
Photo by Mary Sutherland
Descriptions taken from
The Audubon Society Field Guide to North American Rocks and Minerals