metamorphic
Serpentinite (likely)
Serpentine-group minerals, chiefly antigorite/lizardite; commonly with magnetite and relic olivine/pyroxene
AI-generated identification · may be incorrectDark green-gray, mottled and somewhat waxy, with a fine-grained texture and locally metallic or brassy inclusions. Mohs hardness is about 2.5–4; cleavage is poor, luster ranges from waxy to greasy, and specific gravity is roughly 2.5–2.6.
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Physical properties
Dark green-gray, mottled and somewhat waxy, with a fine-grained texture and locally metallic or brassy inclusions. Mohs hardness is about 2.5–4; cleavage is poor, luster ranges from waxy to greasy, and specific gravity is roughly 2.5–2.6.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite undergo hydrothermal metamorphism and hydration, commonly in oceanic crust and subduction zones. Specimen age depends on its source terrane, often Paleozoic to Mesozoic or younger.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as a source of asbestos-bearing serpentine; attractive pieces are collected. Avoid cutting or sanding unknown material because some serpentinite contains chrysotile asbestos.
Geological facts
The pale brassy patch may be sulfide mineralization, possibly pyrite or chalcopyrite, while the small bright inclusion could be quartz or calcite. Serpentinite is California’s state rock.
Field identification & locations
Identify by green-black mottling, waxy feel, low hardness, and association with veins or metallic minerals; it may scratch glass poorly or not at all. Common in Alpine-type ophiolites and subduction belts worldwide.
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