metamorphic
Serpentinite (likely)
Serpentinite, dominated by serpentine-group minerals (chrysotile, lizardite, or antigorite), commonly with magnetite and relict olivine/pyroxene
AI-generated identification · may be incorrectDark green to gray-green, mottled and waxy to dull luster; typically massive with no obvious crystals. Hardness is about 2.5–4 Mohs, though associated olivine or magnetite may be harder and magnetic.
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Physical properties
Dark green to gray-green, mottled and waxy to dull luster; typically massive with no obvious crystals. Hardness is about 2.5–4 Mohs, though associated olivine or magnetite may be harder and magnetic.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, commonly along oceanic crust and plate boundaries. Individual pieces cannot be assigned a geological age from appearance alone.
Uses & applications
Used as decorative stone, carving material, aggregate, and historically as a source of asbestos-bearing serpentine; attractive polished material is collected, though fibrous varieties require health precautions.
Geological facts
Its green color commonly results from serpentine minerals, while black flecks may be magnetite. It can resemble greenstone, basalt, or chlorite-rich rocks.
Field identification & locations
Look for a soft, dense, green-black rock with waxy surfaces, irregular fracture, and occasional magnetic response; a streak, hardness, and thin-section test would confirm it. Common in California, Italy, New Zealand, Canada, and ophiolite belts worldwide.
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