metamorphic

Tumbled serpentinite (likely antigorite-rich)

Serpentinite; chiefly serpentine-group minerals, commonly antigorite, Mg₃Si₂O₅(OH)₄, with magnetite and minor carbonates

AI-generated identification · may be incorrect

Typically mottled olive, gray, yellow, or brown with a waxy to greasy luster; Mohs hardness about 2.5–4, massive and nonfoliated, with variable specific gravity around 2.5–2.6. The polished/tumbled surface shows characteristic veining and mesh-like patterns.

Identified September 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when ultramafic mantle rocks such as peridotite are hydrated during tectonic alteration, commonly in oceanic crust and subduction zones. Individual serpentinite bodies range from Precambrian to modern tectonic settings; this specimen’s age cannot be determined visually.

Uses & applications

Used as an ornamental and carving stone, decorative aggregate, and historically as a heat-resistant material; attractive pieces are sold as lapidary specimens and occasionally jewelry.

Geological facts

Its dark veins may contain magnetite, making some pieces weakly magnetic. Fibrous chrysotile can occur in serpentinite, so avoid drilling, sanding, or creating dust unless the material is tested and handled safely.

Field identification & locations

Identify by its low hardness, waxy feel, green-gray/yellow coloration, convoluted veins, and possible weak magnetism; common in California, Italy, New Zealand, Canada, and many ophiolite belts. Likely value: about $5–$30 as a common tumbled specimen, or $30–$100+ for an unusually patterned polished piece.