Serpentinite

Physical Properties

Hardness: 3-6 Mohs. Color: Typically shades of green (pale to dark), yellow, or grey. Luster: Waxy, greasy, or silky. Structure: Often massive or fibrous. Cleavage: Poor to none (fractures easily along planes of weakness). Specific Gravity: 2.2–2.9.

Formation & Geological History

Formed via serpentinization, a process where ultramafic rocks (like Peridotite) from the Earth's mantle are hydrated at low temperatures and high pressures, often near tectonic plate boundaries and seafloor spreading centers.

Uses & Applications

Used as decorative stone in architecture, as a source of magnesium, and historically as fireproof insulation (when fibrous chrysotile is present). Carvings and ornamental jewelry are common.

Geological Facts

Serpentinite is the official State Rock of California. It can contain small amounts of rare minerals and is sometimes associated with asbestos, which requires careful handling if the specimen is friable or fibrous.

Field Identification & Locations

Identify in the field by its distinct green color, greasy 'soapy' feel, and frequent occurrence in suture zones of mountain belts. Found in the Coast Ranges of California, Italy, Greece, and New Zealand.

Identified on: 4/16/2026

Mode: Standard