Calcite (thing)

Calcite is perhaps one of the most common minerals in the world. It comprises about 4% by weight of the Earth's crust and can be found all over the world. Calcite, when found in crystals and not en masse, can be in more than 300 different forms. Most often, calcite is found in rhombohedral, prismatic or scalenohedral forms. However, over 1,100 shapes of calcite have been seen.

Calcite, which gets its name from the Greek word for lime, chalix, is commonly found in white, yellow, pink, or clear crystals. The pink color sometimes found is from concentrations of manganese in the stone. Clear calcite which is highly doubly refractive is called Iceland Spar, as it was first found in Iceland. Because calcite is so common, it has several different names and types, such as bruyerite, hematoconite, manganoan calcite, onyx-marble, pelagosite, prasochrome, and satin spar. Calcite will often be flourescent when placed underneath a black light or other source of ultra-violet light.

Calcite is formed inside hydrothermal vents, as well as in sedimentary limestones and speleothemes in caves. Rarely it will be found in syenitic or pegmatitic igneous rocks. Calcite is also a large constituent of marble, and can be found in several other rocks and minerals. When in other rocks and minerals, calcite is often white and opaque. Geographically, calcite is found all over the world, Brazil, Germany, Iceland, Cornwall, Bombay, the Harz mountains, Missouri, Oklahoma, Kansas and Wisconsin, to name a few locations.

Sources:
Precious Stones, by Dr. Max Bauer. Charles E. Tuttle Company: Rutland Vermont and Tokyo, Japan, 1969
Gemstones of the World, by Walter Schumann. Sterling Publishing Co., New York, 1979
Simon and Schuster's guide to Rocks and Minerals, Simon and Schuster Inc. New York, 1978
http://mineral.galleries.com/minerals/carbonat/calcite/calcite.htm
http://www.mindat.org/min-859.html