Calcite, Limestone And Marble | Earth Sciences Museum

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Kelly Snyder and Peter Russell

Calcite: A mineral consisting largely of calcium carbonate (CaCO3 ). Next to quartz, it is the most abundant of the Earth's minerals. Crystallizing in the hexagonal system, calcite is noted for its wide variety of crystalline forms.

Calcite is colourless or white when pure, but it may be of almost any colour - reddish, pink, yellow, greenish, blueish, lavender, black, or brown, owing to the presence of diverse impurities. It may be transparent, translucent, or opaque. Its luster ranges from vitreous to dull; many crystals, especially the colourless ones, are vitreous, whereas granular masses, especially those that are fine-grained, tend to be dull. Calcite is number 3 on the Mohs hardness scale; it can be scratched readily by a knife blade or geologic pick. It has a specific gravity of 2.71. Three perfect cleavages give calcite its six-sided polyhedrons with diamond shaped faces; the angles defining the faces are 78 and 102 degrees.

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