metamorphic
Greenstone, likely serpentine
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with dark magnetite/chromite or pyroxene inclusions
AI-generated identification · may be incorrectUsually Mohs 2.5–4, green to black mottled color, waxy to greasy luster, fine-grained and massive rather than visibly crystalline; no prominent cleavage. The rounded shape appears tumbled or naturally worn.
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Physical properties
Usually Mohs 2.5–4, green to black mottled color, waxy to greasy luster, fine-grained and massive rather than visibly crystalline; no prominent cleavage. The rounded shape appears tumbled or naturally worn.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, commonly along tectonic plate boundaries and faults. Formation ages vary widely, from ancient Precambrian bodies to modern oceanic settings.
Uses & applications
Used as ornamental stone, carvings, beads, and occasionally architectural material; attractive specimens have modest lapidary value.
Geological facts
Dark specks may be magnetite, chromite, or relict pyroxene. Serpentinite can resemble jade, but it is generally softer and less dense; some varieties contain asbestos-form minerals and should not be cut or powdered without proper controls.
Field identification & locations
Identify by its mottled apple-green/black appearance, waxy feel, low hardness, and commonly slick surfaces; common in California, the Appalachians, New Zealand, Italy, and ophiolite belts worldwide. A definitive ID requires hardness, streak, density, and possibly microscopy or Raman testing.
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