metamorphic
Serpentinite (polished/tumbled)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with magnetite and remnants of olivine/pyroxene
AI-generated identification · may be incorrectTypically mottled dark green, yellow-green, black, and gray with waxy to subvitreous luster; Mohs hardness 2.5–5.5, massive rather than visibly crystalline, and commonly lacking obvious cleavage. The specimen’s rounded, polished surface and green-black veining fit serpentinite.
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Physical properties
Typically mottled dark green, yellow-green, black, and gray with waxy to subvitreous luster; Mohs hardness 2.5–5.5, massive rather than visibly crystalline, and commonly lacking obvious cleavage. The specimen’s rounded, polished surface and green-black veining fit serpentinite.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, often along oceanic crust and fault zones. Formation ages vary widely; the rock may be Paleozoic to Mesozoic or younger depending on its source.
Uses & applications
Used as decorative and carving stone, countertops, tiles, cabochons, and ornamental tumbled material; historically marketed as “serpentine marble.” Avoid prolonged handling or dust exposure if asbestos-forming fibers are present.
Geological facts
Its mottled pattern results from serpentinization and associated magnetite formation, which can make some pieces weakly magnetic. It may resemble jade, but is generally softer and less tough.
Field identification & locations
Identify by green-black mottling, waxy polish, low hardness, and occasional magnetism; a steel knife may scratch it, unlike jade. Common in ophiolites and ultramafic belts, including California, Italy, New Zealand, and Canada.
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