metamorphic
Likely serpentinite
Serpentinite, composed mainly of serpentine-group minerals (antigorite, lizardite, chrysotile), commonly with magnetite and minor chromite
AI-generated identification · may be incorrectDark greenish-gray, mottled and fine-grained with a dull to waxy luster; hardness about 2.5–4 Mohs, poor cleavage, and specific gravity roughly 2.5–2.7. The pale vein is likely carbonate or fibrous serpentine.
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Physical properties
Dark greenish-gray, mottled and fine-grained with a dull to waxy luster; hardness about 2.5–4 Mohs, poor cleavage, and specific gravity roughly 2.5–2.7. The pale vein is likely carbonate or fibrous serpentine.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during low-temperature metamorphism and seafloor alteration. It occurs in ophiolites and subduction-zone mélanges, ranging from ancient Precambrian bodies to young tectonic belts.
Uses & applications
Used as decorative and architectural stone, countertops, carvings, and occasionally as a source of magnesium or asbestos-group minerals. The pictured rough fragment has little commercial value.
Geological facts
Serpentinite often has a slick, waxy feel and may show a pronounced green-black mottling. Some varieties contain chrysotile, so cutting or grinding unknown specimens should be avoided due to potential asbestos fibers.
Field identification & locations
Common in California, Italy, Greece, New Zealand, the Canadian Appalachians, and other ophiolite belts. Confirm with a streak, hardness, magnetism, and ideally thin-section or X-ray analysis; visual identification is provisional.
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