Serpentine
Mg3Si2O5(OH)4

Serpentine, common, widely distributed mineral, composed of hydrated magnesium silicate, Mg3Si2O5(OH)4, so called because of serpentlike bands of green color occurring in massive varieties. It crystallizes in the monoclinic system and occurs in two distinct forms: antigorite, a massive variety, and chrysotile, a fibrous variety. The massive variety has a greasy, waxy luster, and the fibrous variety is silky. Both varieties are colored light and dark green, which in massive formations of antigorite produce a beautiful, variegated coloring. The term serpentine is also applied to a rock composed principally of antigorite. The hardness of the mineral ranges from 2 to 5, and the specific gravity ranges from 2.2 for chrysotile to 2.65 for antigorite. Chrysotile is the mineral from which asbestos is made. Antigorite, often used as an ornamental stone, sometimes occurs as a collateral mineral in verd antique marble.

Serpentine always occurs as an alteration product of another magnesium silicate mineral, such as olivine, amphibole, or pyroxene. Large deposits of chrysotile are located in Canada, in Russia, in Kazakhstan, in South Africa, and in Vermont, New York, New Jersey, and Arizona in the United States.

Source: (http://encarta.msn.com)