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             Calcite, a carbonate mineral, is calcium carbonate and is one of the most widely distributed minerals on the Earth's surface. It is a common constituent of sedimentary rocks, limestone in particular.  It is also the primary mineral in metamorphic marble. Calcite occurs as a vein mineral in deposits from hot springs, and in caverns as stalactites and stalagmites.  Calcite is transparent to opaque and may occasionally show phosphorescence or fluorescence.  It is perhaps best known because of its power to produce strong double refraction of light, such that objects viewed through a clear piece of calcite appear doubled in all of their parts.  Calcite exhibits an unusual characteristic called retrograde solubility in which it becomes less soluble in water as the temperature increases.  When conditions are right for precipitation, calcite forms mineral coatings that cement the existing rock grains together or it can fill fractures.[i]