metamorphic
Serpentine-rich greenstone
Serpentinite, dominated by serpentine-group minerals (antigorite/lizardite/chrysotile), with possible chlorite, magnetite, and talc
AI-generated identification · may be incorrectTypically olive to apple-green, mottled, waxy to greasy luster, fine-grained and massive; Mohs hardness about 2.5–4, generally lacking visible crystals and having irregular fractures. The rounded surface reflects beach abrasion rather than natural crystal form.
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Physical properties
Typically olive to apple-green, mottled, waxy to greasy luster, fine-grained and massive; Mohs hardness about 2.5–4, generally lacking visible crystals and having irregular fractures. The rounded surface reflects beach abrasion rather than natural crystal form.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated and metamorphosed, commonly along oceanic crust and tectonic shear zones; ages vary widely. This specimen is likely a glacially or wave-rounded cobble from a serpentinite-bearing coastal deposit.
Uses & applications
Used as decorative stone, carvings, countertops, and historical tools; attractive pieces are collected, though fibrous chrysotile-bearing material should not be cut or powdered because of asbestos risk.
Geological facts
Serpentinite is California’s state rock and commonly preserves the chemical effects of water interacting with mantle rock. Dark specks may be magnetite, and rusty patches commonly represent iron oxidation.
Field identification & locations
Identify it by its green mottling, low hardness, waxy feel, and unusually light-to-moderate weight compared with many dark igneous rocks; a streak, hardness, and magnet test can help. Common in California, New Zealand, Italy, the Alps, and ophiolite belts worldwide.
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