metamorphic
Tumbled greenstone (likely serpentine or nephrite jade)
Serpentine-group minerals, commonly antigorite; possibly nephrite, a fibrous aggregate of amphibole (actinolite–tremolite)
AI-generated identification · may be incorrectDark green, opaque, waxy to dull luster with pale veining; rounded and polished. Hardness is about 2.5–4 for serpentine or 6–6.5 for nephrite; no visible crystal structure, typically massive and compact.
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Physical properties
Dark green, opaque, waxy to dull luster with pale veining; rounded and polished. Hardness is about 2.5–4 for serpentine or 6–6.5 for nephrite; no visible crystal structure, typically massive and compact.
Formation & geological history
Serpentine forms by hydrothermal alteration of ultramafic mantle rocks, commonly in ophiolites; nephrite forms through metamorphism and metasomatism. Exact age and locality cannot be determined from the photograph.
Uses & applications
Used as a tumbled ornamental stone, carving material, and occasionally jewelry; nephrite-quality material is more valuable and durable than ordinary serpentine.
Geological facts
The term “greenstone” is informal and can include serpentine, nephrite, bowenite, and other green rocks. Pale crack-like lines may be natural veining or healed fractures emphasized by polishing.
Field identification & locations
Likely serpentine if it feels relatively soft and scratches with a steel blade; nephrite resists scratching and has a tough, fibrous texture. Common sources include California, New Zealand, British Columbia, Russia, and China.
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