Serpentine, a common rock-forming mineral. Serpentine is a hydrous magnesium silicate, consisting of magnesium, silicon, oxygen, and hydrogen. It has a greasy feel, and is easily scratched with a knife. Serpentine is usually some shade of green, but may be red, yellow, white, brown, or black. It often has a mottled, or spotted, appearance because of impurities, and is translucent or opaque. (It was named for the serpentlike patterns of the green, mottled varieties.) Most forms of serpentine have a waxy luster. Some translucent varieties are used in jewelry and in making small ornamental objects. Chrysolite, a fibrous variety, has a silky luster and can be easily separated into fine fibers. It is the chief source of asbestos.

The term serpentine is also applied to rocks composed chiefly of the mineral serpentine. When polished, some forms of serpentine rock resemble marble. They are widely used as ornamental building stone.

Serpentine is usually found associated with magnesium silicates such as olivine and various pyroxenes and amphiboles, and as grains in both igneous and metamorphic rocks. Most chrysotile is mined in Russia and Canada. Serpentine rock of great beauty is obtained from Great Britain, Ireland, Italy, France, and Greece.

Chemical formula: Mg6Si4O10(OH)8. Specific gravity: 2.2 to 2.65. Hardness; 2 to 5.