metamorphic

Polished bronzite-rich serpentinized rock

Serpentinite or serpentinized peridotite, likely containing bronzite (orthopyroxene) and magnetite

AI-generated identification · may be incorrect

Dark brown, bronze, and black mottling with a silky to waxy polished luster; typically Mohs 3–6 depending on alteration, with a fine-grained massive texture and no visible cleavage. Specific gravity is commonly about 2.6–3.3.

Identified September 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when ultramafic mantle rock, chiefly peridotite, was hydrated and metamorphosed to serpentine minerals, often with residual pyroxene and magnetite. Such rocks commonly formed in oceanic crust and ophiolite zones from the Precambrian to the present.

Uses & applications

Used as a decorative stone, carving and cabochon material, and sometimes architectural facing stone; polished specimens are mainly collected for appearance.

Geological facts

The bronze sheen commonly comes from bronzite or fibrous serpentine surfaces, while black flecks may be magnetite or chromite. Strong magnetism, if present, supports an ultramafic composition.

Field identification & locations

Common in serpentinite belts and ophiolites, including California, Vermont, Italy, New Zealand, and Oman; identify by its green-brown waxy appearance, heavy feel, and possible magnetism. Exact identification requires hardness, streak, and thin-section or chemical testing.