metamorphic
Tumbled dark green stone, likely serpentine or nephrite jade
Serpentine-group minerals, chiefly antigorite/lizardite; possibly nephrite, an aggregate of tremolite–actinolite
AI-generated identification · may be incorrectDark green, opaque, smoothly polished with a waxy to dull luster; hardness is about 2.5–4 for serpentine or 6–6.5 for nephrite, with no visible cleavage and a fine-grained massive texture. The photograph alone cannot reliably distinguish these materials.
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Physical properties
Dark green, opaque, smoothly polished with a waxy to dull luster; hardness is about 2.5–4 for serpentine or 6–6.5 for nephrite, with no visible cleavage and a fine-grained massive texture. The photograph alone cannot reliably distinguish these materials.
Formation & geological history
Serpentine forms when ultramafic rocks undergo hydration during hydrothermal metamorphism; nephrite forms through metamorphic alteration of mafic or ultramafic rocks. These processes occur across many geological ages, commonly in ancient mountain belts.
Uses & applications
Tumbled pieces are used as ornamental stones, carvings, cabochons, and curios; nephrite is also used for durable jewelry and sculpture. Serpentine has limited architectural and decorative use.
Geological facts
A strong candidate for serpentine can be tested with a steel file: it usually scratches readily, whereas nephrite generally resists. Acid testing is not diagnostic; professional gemological testing is needed for identification.
Field identification & locations
Common sources include New Zealand, China, Canada, Russia, Italy, and the United States. Typical tumbled specimens are worth about $2–$15; attractive verified nephrite may bring $20–$200 or more.
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