metamorphic
Tumbled dark green stone, likely serpentine or greenstone
Serpentine-group minerals, chiefly antigorite/lizardite; possibly chlorite-rich greenstone
AI-generated identification · may be incorrectOpaque dark olive-green, waxy to dull luster, fine-grained and rounded by tumbling; hardness typically Mohs 2.5–4, with no visible cleavage or crystals. Identification is uncertain from the photograph alone.
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Physical properties
Opaque dark olive-green, waxy to dull luster, fine-grained and rounded by tumbling; hardness typically Mohs 2.5–4, with no visible cleavage or crystals. Identification is uncertain from the photograph alone.
Formation & geological history
Serpentine forms when ultramafic mantle rocks hydrate during tectonic alteration, commonly in ancient ophiolites and subduction zones. Greenstone may instead represent metamorphosed basalt; age varies widely by locality.
Uses & applications
Commonly sold as inexpensive tumbled material, carvings, and decorative stone; serpentine is also used for ornaments and architectural objects. It is generally unsuitable for high-wear jewelry because of its low hardness.
Geological facts
Serpentine’s green color comes from iron and nickel-bearing minerals; some varieties may contain chrysotile asbestos, so avoid cutting, drilling, or creating dust unless tested. A magnet or hardness test can help distinguish possibilities.
Field identification & locations
Look for a greasy or waxy feel, mottled olive-green color, low hardness, and possible white veining. Common sources include California, New Zealand, Italy, Canada, and Afghanistan; definitive identification requires hardness, streak, density, and possibly microscopy or Raman analysis.
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