serpentin

Serpentin, or serpentine, is a group of hydrous magnesium silicate minerals that form by the hydration of ultramafic rocks in a process known as serpentinization. The group comprises several minerals with similar composition but different crystal structures, most notably antigorite, chrysotile, and lizardite.

Chemically, serpentine minerals are magnesium silicates with variable iron content and a water component. They are typically greenish, pale green to colorless, and display a greasy or silky luster. The hardness on the Mohs scale ranges roughly from 2.5 to 4, and the specific gravity is commonly between 2.5 and 3.5. Serpentine minerals occur as massive rocks, as fibrous aggregates in chrysotile, or as sheet-like crystals.

Formation and occurrence: Serpentine minerals form during serpentinization, a low-temperature hydration reaction of ultramafic rocks such as peridotite and dunite, often in tectonically active settings like ophiolites or subduction zones. Serpentinite rock is the aggregate of these minerals and is widespread in regions where ultramafic rocks have been altered by fluids.

Uses and significance: Serpentine rocks are used as ornamental stone and for sculpture. The fibrous variety chrysotile has been used historically as asbestos, but inhalation of respirable fibers poses health risks. Serpentine soils, derived from weathered serpentinite, are typically low in calcium and rich in magnesium and certain heavy metals, which can influence plant communities and agriculture.

Etymology: The name derives from the Latin serpens, meaning serpent, in reference to the stone’s serpentine patterns and green color.