metamorphic
Tumbled greenstone (likely serpentine or nephrite jade)
Serpentine-group minerals, chiefly antigorite/lizardite; possibly nephrite, a fibrous tremolite–actinolite aggregate
AI-generated identification · may be incorrectOpaque dark green, waxy to greasy luster, smooth polished surface, fine-grained massive texture, and no visible cleavage. Serpentine has Mohs hardness about 2.5–4; nephrite is harder, about 6–6.5, with specific gravity roughly 2.5–3.0.
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Physical properties
Opaque dark green, waxy to greasy luster, smooth polished surface, fine-grained massive texture, and no visible cleavage. Serpentine has Mohs hardness about 2.5–4; nephrite is harder, about 6–6.5, with specific gravity roughly 2.5–3.0.
Formation & geological history
Serpentine forms when ultramafic mantle rocks are hydrated during metamorphism; nephrite forms through metasomatic metamorphism. Such rocks commonly formed during Precambrian to Mesozoic tectonic events, depending on locality.
Uses & applications
Used as ornamental stone, carvings, cabochons, tumbled stones, and occasionally architectural facing; gem-quality nephrite is valuable for jewelry and sculpture.
Geological facts
The photograph shows a polished/tumbled specimen, so key diagnostic features such as grain and cleavage are obscured. Color alone cannot reliably distinguish inexpensive serpentine from jade.
Field identification & locations
Common sources include California, Washington, British Columbia, New Zealand, China, and Central Asia. A scratch test, density measurement, magnification, and professional refractive-index or spectroscopy testing are needed for reliable identification.
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