A mineral is a naturally-occurring, solid, inorganic, crystalline substance having a fairly definite chemical composition and having fairly definite physical properties. At its simplest, a mineral is a naturally-occurring solid chemical. Currently, there are over 6000 named and described minerals - about 200 of them are common and about 20 of them are very common. Mineral classification is based on anion chemistry. Major categories of minerals are: elements, sulfides, oxides, halides, carbonates, sulfates, phosphates, and silicates.
The carbonate minerals all contain one or more carbonate (CO3-2) anions.
Calcite is a common mineral. It is calcium carbonate (CaCO3). It has a nonmetallic luster, commonly clearish to whitish to yellowish to grayish in color, is moderately soft (H≡3), moderately light-weight, has six-sided crystals (calcite is actually in the trigonal crystal system - crystals of calcite are often scalenohedrons), and rhombohedral cleavage (three cleavage planes at 75º & 105º angles - cleavage pieces look like lopsided boxes). The easiest way to identify calcite is to drop acid on it - it easily bubbles (effervesces) in acid. The bubbles are carbon dioxide gas. If the acid is dilute hydrochloric acid, the chemical reaction is:
2HCl(aq) + CaCO3(s) -->> CO2(g)↑ + H2O(l) + CaCl2(aq)
The most important and voluminous calcitic rocks in the world are limestone (sedimentary), marble (metamorphic), carbonatite (igneous), and travertine (speleothem, or "cave formations", and many hotspring deposits). Many hydrothermal veins in the world are calcitic or have calcite as a principal component.
Locality: Stoneco Incorporated Maumee Quarry, town of Maumee, Lucas County, northwestern Ohio, USA
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Photo gallery of calcite:
www.mindat.org/gallery.php?min=859
