metamorphic
Tumbled serpentinite (likely)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with dark magnetite/chromite and pale carbonate or talc veins
AI-generated identification · may be incorrectMohs hardness about 2.5–4; mottled dark green, black, gray, and cream; waxy to dull luster; fine-grained, massive texture with no visible cleavage. The rounded shape indicates tumbling or water wear.
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Physical properties
Mohs hardness about 2.5–4; mottled dark green, black, gray, and cream; waxy to dull luster; fine-grained, massive texture with no visible cleavage. The rounded shape indicates tumbling or water wear.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated during hydrothermal alteration, commonly along oceanic crust and tectonic plate boundaries. Most examples are Paleozoic to younger, though age cannot be determined from the photograph.
Uses & applications
Used as decorative stone, carvings, beads, and polished specimens; historically used locally as building stone. Value is generally modest unless unusually patterned or from a notable locality.
Geological facts
Serpentinite is named for its often snakeskin-like mottling and may contain magnetite, giving some pieces weak magnetic response. It can be confused with dark green marble, soapstone, or gabbro.
Field identification & locations
Look for a green-black mottled appearance, waxy feel, low hardness, and possible magnetism; a steel blade may scratch it. Common sources include California, Italy, New Zealand, Canada, and Scotland.
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