metamorphic
Serpentine (likely antigorite-rich serpentinite)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with dark magnetite/chromite or pyroxene inclusions
AI-generated identification · may be incorrectGreen to yellow-green, mottled black, waxy to slightly greasy luster, and fine-grained massive texture; Mohs hardness about 2.5–4, with no visible cleavage and specific gravity around 2.5–2.6. The rounded, polished surface appears water-worn or tumbled.
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Physical properties
Green to yellow-green, mottled black, waxy to slightly greasy luster, and fine-grained massive texture; Mohs hardness about 2.5–4, with no visible cleavage and specific gravity around 2.5–2.6. The rounded, polished surface appears water-worn or tumbled.
Formation & geological history
Forms when magnesium-rich ultramafic rocks such as peridotite hydrate during seafloor alteration or tectonic metamorphism. It commonly formed in ancient oceanic mantle and is exposed in ophiolite belts, often Paleozoic to Mesozoic or older.
Uses & applications
Used as ornamental stone, carvings, beads, countertops, and historically as a decorative marble substitute; some varieties are collected as lapidary material. Avoid generating dust because asbestos-group minerals can occur in some serpentinites.
Geological facts
Its mottled green-black pattern is characteristic of serpentinization, a reaction that converts olivine and pyroxene to serpentine minerals. Magnetite produced during alteration may make pieces weakly magnetic.
Field identification & locations
Common in California, the Appalachians, New Zealand, Italy, Canada, and other ophiolite regions; it is identified by its green color, low hardness, waxy feel, and reaction to a steel knife. A precise identification would require hardness, streak, magnetism, or microscopy.
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