Calcite

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Other names: Iceland Spar (found in basalt caves), Island Spar, Calc spar
Mineral class: Carbonate
Composition: CaCO₃, just like shells, bones, teeth, chalk, limestone, marble.
Hardness: 3
Luster: Glassy, Pearly, Vitreous
Color: Colorless, White, grey
Streak: White
Cleavage: Perfect, 3 planes not at right angles
Specific Gravity: 2.71
Crystal form: More than 300 crystal forms. Usually hexagonal: rhombohedral, scalenohedral or prismatic crystals (use magnifying lens if necessary to spot them).
Environment: Chemically precipitates from high concentrations of calcium bicarbonate (Ca₂₊ + H₂CO₃), forming speleothems in caves (stalactites, stalagmites, helictites, soda straws, etc.) or travertine deposits from spring water. Also forms limestone, marble, chalk, tufa, and other rocks. May act as a cementing agent for sedimentary rocks, or form concretions within sedimentary formations (as well as septaria and crystals in geodes).
Uses: Fertilizer, marble sculpture and building material, myriad mineralogical, chemical and other industrial uses. Lime for mortar and fertilizer.
Comments:
Scratched by knife but not fingernail.
Golden-yellow crystals 1 meter long have been found in Joplin, Missouri, and Pitcher, Oklahoma.
Infusible: dissociates on heating to form lime (CaO) and carbon dioxide (CO₂).
Optical property of double refraction was explained by Isaac Newton in his Opticks.
Reacts briskly with dilute hydrochloric acid. For this reason geologists carry bottles of dilute HCl with them in the field, to distinguish calcite and calcium carbonate rocks from quartz, barite, gypsum, dolomite, and other white rocks.
Chief mineral in limestone.
[calcite.jpg] [travertine.jpg]

Other names:	Iceland Spar (found in basalt caves), Island Spar, Calc spar
Mineral class:	Carbonate
Composition:	CaCO₃, just like shells, bones, teeth, chalk, limestone, marble.
Hardness:	3
Luster:	Glassy, Pearly, Vitreous
Color:	Colorless, White, grey
Streak:	White
Cleavage:	Perfect, 3 planes not at right angles
Specific Gravity:	2.71
Crystal form:	More than 300 crystal forms. Usually hexagonal: rhombohedral, scalenohedral or prismatic crystals (use magnifying lens if necessary to spot them).
Environment:	Chemically precipitates from high concentrations of calcium bicarbonate (Ca₂₊ + H₂CO₃), forming speleothems in caves (stalactites, stalagmites, helictites, soda straws, etc.) or travertine deposits from spring water. Also forms limestone, marble, chalk, tufa, and other rocks. May act as a cementing agent for sedimentary rocks, or form concretions within sedimentary formations (as well as septaria and crystals in geodes).
Uses:	Fertilizer, marble sculpture and building material, myriad mineralogical, chemical and other industrial uses. Lime for mortar and fertilizer.
Comments:	Scratched by knife but not fingernail. Golden-yellow crystals 1 meter long have been found in Joplin, Missouri, and Pitcher, Oklahoma. Infusible: dissociates on heating to form lime (CaO) and carbon dioxide (CO₂). Optical property of double refraction was explained by Isaac Newton in his Opticks. Reacts briskly with dilute hydrochloric acid. For this reason geologists carry bottles of dilute HCl with them in the field, to distinguish calcite and calcium carbonate rocks from quartz, barite, gypsum, dolomite, and other white rocks. Chief mineral in limestone.