metamorphic
Serpentinite (likely)
Serpentinite; predominantly serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite and relic olivine/pyroxene
AI-generated identification · may be incorrectDark green-black, mottled and subtly waxy to greasy luster with yellow-green veins; typically massive and fine-grained, Mohs hardness about 2.5–4, with no obvious cleavage and specific gravity roughly 2.5–2.7. The specimen may also contain harder, metallic-looking sulfides or accessory minerals.
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Physical properties
Dark green-black, mottled and subtly waxy to greasy luster with yellow-green veins; typically massive and fine-grained, Mohs hardness about 2.5–4, with no obvious cleavage and specific gravity roughly 2.5–2.7. The specimen may also contain harder, metallic-looking sulfides or accessory minerals.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism, commonly along oceanic crust and fault zones. Ages range from Precambrian to modern tectonic settings; precise age cannot be determined visually.
Uses & applications
Used as decorative stone, carvings, countertops, and historically as a source of ornamental “verde antique”; collectors value attractive veining and polish. Chrysotile-bearing material should not be cut, drilled, or powdered because its dust can be hazardous.
Geological facts
Serpentinite records interaction between rock and water and can host unusual chromium-, nickel-, and cobalt-rich minerals. Its dark green color and slick-looking surfaces commonly result from serpentine minerals and magnetite.
Field identification & locations
Identify it by its green-black mottling, waxy feel, low hardness, and possible magnetism; a streak, hardness, acid, and thin-section test would help confirm it. Common occurrences include California, Italy, New Zealand, Canada, and many former oceanic-rock belts.
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