metamorphic
Serpentinite (serpentine-rich rock)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with possible magnetite, chlorite, and talc
AI-generated identification · may be incorrectDark gray-green, mottled and locally waxy with a fine to coarse crystalline texture; serpentine has Mohs hardness 2.5–4, nonmetallic to greasy luster, and commonly lacks strong cleavage. The green translucent patches may be antigorite or chrysotile; exact identification requires testing.
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Physical properties
Dark gray-green, mottled and locally waxy with a fine to coarse crystalline texture; serpentine has Mohs hardness 2.5–4, nonmetallic to greasy luster, and commonly lacks strong cleavage. The green translucent patches may be antigorite or chrysotile; exact identification requires testing.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism and seafloor or subduction-zone alteration. It commonly formed during ancient oceanic crust and mountain-building events, with age varying by locality.
Uses & applications
Used as decorative stone, facing material, carvings, and occasionally crushed aggregate; attractive polished pieces are collected, though fibrous chrysotile-bearing material should not be cut or powdered.
Geological facts
Often contains magnetite, making some specimens weakly magnetic. It is California’s state rock and is associated with tectonic plate boundaries and ophiolite complexes.
Field identification & locations
Identify by its dark green-black mottling, relatively low hardness, waxy feel, and possible magnetism; common in California, the Appalachians, New Zealand, Italy, and other ophiolite belts. Confirm with hardness, streak, magnetism, and thin-section or Raman/XRD testing.
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