metamorphic
Polished serpentine (likely greenstone)
Serpentine-group minerals, chiefly antigorite/lizardite: Mg₃Si₂O₅(OH)₄
AI-generated identification · may be incorrectTypically mottled green to black, waxy to greasy luster, hardness about 2.5–4 Mohs, very fine-grained and massive; the specimen appears polished and elongated. Exact identification is uncertain from an image alone, and similar nephrite or altered ultramafic rock is possible.
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Physical properties
Typically mottled green to black, waxy to greasy luster, hardness about 2.5–4 Mohs, very fine-grained and massive; the specimen appears polished and elongated. Exact identification is uncertain from an image alone, and similar nephrite or altered ultramafic rock is possible.
Formation & geological history
Forms when magnesium-rich peridotite is hydrated during low-temperature metamorphism, commonly in ancient oceanic crust and subduction-related belts. Serpentinization occurs from the Precambrian to the present.
Uses & applications
Used as ornamental stone, carvings, beads, cabochons, and occasionally dimension stone; historically called greenstone in some collecting and cultural contexts. It is generally inexpensive unless exceptionally patterned or carved.
Geological facts
Serpentine is a mineral group rather than one single mineral, and its fibrous varieties are related to chrysotile asbestos. Polishing enhances its mottled green, black, and yellow-green patterns.
Field identification & locations
Look for a soft, waxy-feeling, green-black mottled stone that can be scratched by a steel knife; it is usually non-cleaving and dense. Common localities include California, Vermont, New Zealand, Italy, Russia, and Afghanistan.
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