metamorphic
Serpentine-rich metamorphic rock
Serpentinite, likely antigorite/lizardite with accessory magnetite or chromite
AI-generated identification · may be incorrectBlue-green to gray-green, mottled and fine-grained with a waxy to dull luster; typically Mohs 2.5–4, with poor cleavage and a massive, sometimes fibrous texture. The rounded specimen may be naturally weathered or tumbled.
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Physical properties
Blue-green to gray-green, mottled and fine-grained with a waxy to dull luster; typically Mohs 2.5–4, with poor cleavage and a massive, sometimes fibrous texture. The rounded specimen may be naturally weathered or tumbled.
Formation & geological history
Forms when olivine- and pyroxene-rich ultramafic rocks hydrate during low-temperature metamorphism. Serpentinite is common in California’s Coast Ranges, including areas near 36.9°N, 121.4°W, and generally formed during Mesozoic oceanic-plate tectonic processes.
Uses & applications
Used as decorative stone, carving material, aggregate, and historically as a source of asbestos-group minerals; attractive pieces are collected, though this small specimen has limited commercial value.
Geological facts
California’s state rock is serpentine, a rock dominated by serpentine minerals. Some serpentinite can contain naturally occurring asbestos fibers, so avoid sawing, drilling, sanding, or crushing it.
Field identification & locations
Identify by its green color, low hardness, waxy appearance, and occasional black magnetic grains or veining. A streak, hardness, magnetism, and close inspection for fibrous asbestos would improve confidence; regional geology strongly supports this identification.
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