June 2008 Mineral of the Month
Calcite
Found in most geologic settings and, in one form or another, as a later forming replacement mineral in many other environments . It is most common as a massive material in limestones and marbles. It forms as chemical sedimentary deposits in limestone and can be regionally metamorphosed into marbles. Calcite is also a common gangue mineral in hydrothermal deposits. Its crystals are rhombohedral and scalenohedral with combinations producing “nailhead” and “dogtooth” forms. Iceland Spar variety shows double refraction. Twinning is very common.
Its chemical properties are as follows:
Mineral Group......................Carbonates
Chemical formula................CaCO3
Specific Gravity...................2.71
Tenacity…………………….Brittle
Color......................................White, Yellow, Red,
Hardness..............................3
Luster....................................Vitreous, Pearly
Transparency.....................Transparent to Translucent
Streak....................................White to Greyish
Cleavage..............................Perfect
Fracture...............................Subconchoidal
