metamorphic
Tumbled serpentine
Serpentinite; chiefly serpentine-group minerals, Mg3Si2O5(OH)4
AI-generated identification · may be incorrectTypically olive-green to yellow-green with reddish-brown iron staining, waxy to greasy luster, and massive rather than visible crystal structure; Mohs hardness 2.5–4, poor or indistinct cleavage, and specific gravity about 2.5–2.6.
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Physical properties
Typically olive-green to yellow-green with reddish-brown iron staining, waxy to greasy luster, and massive rather than visible crystal structure; Mohs hardness 2.5–4, poor or indistinct cleavage, and specific gravity about 2.5–2.6.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, commonly along oceanic crust and subduction zones; many specimens are Paleozoic to younger. The rounded shape indicates human tumbling and polishing.
Uses & applications
Used as ornamental stone, carvings, cabochons, beads, and sometimes architectural material; historically used for decorative objects. Fibrous varieties may contain asbestos and should not be cut or powdered without testing.
Geological facts
The mottled green, yellow, and red coloration is characteristic of serpentine altered by iron oxidation. It is California’s state rock, although some similar-looking stones are nephrite, jasper, or soapstone.
Field identification & locations
Identify by its low hardness, waxy feel, green mottling, and inability to scratch glass; a streak, hardness, and asbestos-mineral test can help confirm it. Common in California, Italy, New Zealand, Canada, and ultramafic terranes worldwide.
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