Monday, May 26, 2008

Del Air Rockhounds Present............

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................CaCO
3
Specific Gravity...................2.71
Tenacity…………………….Brittle
Color......................................White, Yellow, Red,
Orange, Blue, Green, Brown, and Grey
Hardness..............................3

Luster....................................Vitreous, Pearly
Transparency.....................Transparent to Translucent
Streak....................................White to Greyish
Cleavage..............................Perfect
Fracture...............................Subconchoidal