metamorphic
Serpentinite (serpentine-rich rock)
Serpentinite; chiefly serpentine-group minerals, Mg₃Si₂O₅(OH)₄, with possible magnetite, brucite, and talc
AI-generated identification · may be incorrectPale green, mottled and waxy to dull luster, massive rather than visibly crystalline; typically Mohs hardness 2.5–4, poor cleavage, and specific gravity about 2.5–2.6. The rusty brown patches likely represent iron oxidation or minor magnetite.
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Physical properties
Pale green, mottled and waxy to dull luster, massive rather than visibly crystalline; typically Mohs hardness 2.5–4, poor cleavage, and specific gravity about 2.5–2.6. The rusty brown patches likely represent iron oxidation or minor magnetite.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated by low-temperature hydrothermal fluids, commonly in oceanic crust and tectonic suture zones. Individual specimens may be Paleozoic to modern in age, depending on the host terrane.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as a source of magnesium; attractive varieties are collected, though asbestos-bearing forms require caution when cutting or sanding.
Geological facts
Often displays a characteristic green ‘scaly’ or mottled appearance and may feel unusually soft and smooth. Some serpentinite contains chrysotile or other fibrous asbestos minerals.
Field identification & locations
Common in California, the Appalachians, the Alps, New Zealand, and ophiolite belts worldwide. Identify by its green color, waxy surface, softness, and association with dark ultramafic rocks; exact identification requires testing or microscopy.
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