Serpentine

Serpentine is not a single mineral but a group of closely related magnesium phyllosilicates sharing the formula Mg3Si2O5(OH)4, including antigorite, chrysotile, and lizardite. These polymorphs form through low-grade metamorphic alteration of olivine, orthopyroxene, and other magnesium-rich minerals in ultramafic rocks, giving rise to the rock type known as serpentinite. Colors range from deep bottle-green and yellow-green to mottled black and brown, often displaying the swirling, veined patterns that made massive serpentine prized as an ornamental and carving stone since antiquity, sometimes marketed as verd antique when veined with white carbonate or quartz.

Type localities anchor the group's history: lizardite takes its name from the Lizard Peninsula in Cornwall, England, long celebrated for ornamental "noble serpentine" carvings, while antigorite was first described from the Antigorio Valley in Piedmont, Italy, and the nearby Val Malenco district remains a classic Italian Alps source of fine platy antigorite specimens. Chrysotile, the fibrous, silky-lustered variety historically mined as asbestos, reached peak commercial importance at the Jeffrey Mine in Asbestos and at Thetford Mines, both in Quebec, Canada, while Arizona, California's Coast Ranges, and British Columbia have also yielded notable fibrous and massive material. Other important occurrences include Mount Olympus in Cyprus, New Zealand's South Island (source of the translucent bowenite variety), and carving-grade deposits across Afghanistan, Pakistan, China, Russia, and India. Serpentine is commonly associated with talc, chromite, chlorite, and magnesite, and can host nickel to form a series with népouite.

For collectors, serpentine specimens are valued both for mineralogical study of the antigorite–chrysotile–lizardite polytypes, and for their aesthetic, richly textured surfaces that showcase serpentinite's role as a marker of ancient oceanic crust uplifted onto land. Well-crystallized antigorite plates from the Italian Alps, bastite pseudomorphs after enstatite, and pseudomorphs after olivine are especially sought after, alongside polished slabs displaying the classic mottled green-and-black "serpent-skin" pattern that gives the group its name. Whether acquired as a scientific reference specimen or a decorative lapidary piece, serpentine offers remarkable variety within a single mineral family, prized by systematic collectors and rock hounds alike.