metamorphic
Serpentinite (probable)
Serpentinite, dominated by serpentine-group minerals (chrysotile, lizardite, or antigorite), commonly with magnetite
AI-generated identification · may be incorrectTypically dark green to black, mottled, waxy to dull luster, and fine-grained; Mohs hardness is about 2.5–4, with variable density and weak-to-absent cleavage. The specimen’s green-black coloration and coarse, altered appearance are consistent with serpentinite, though image-only identification is tentative.
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Physical properties
Typically dark green to black, mottled, waxy to dull luster, and fine-grained; Mohs hardness is about 2.5–4, with variable density and weak-to-absent cleavage. The specimen’s green-black coloration and coarse, altered appearance are consistent with serpentinite, though image-only identification is tentative.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite are hydrated during seafloor alteration or tectonic activity. It can occur in ancient ophiolites and subduction-zone mélanges; age depends on its host terrane.
Uses & applications
Used as decorative stone, carving material, aggregate, and historically as a source of asbestos-bearing material; jewelry pieces are sometimes polished. Avoid cutting or abrading unknown specimens because some serpentinite contains fibrous asbestos minerals.
Geological facts
Often contains magnetite, giving it a heavy feel and occasional magnetic response. Its green color results from hydration and alteration of magnesium-rich minerals.
Field identification & locations
Look for green-black mottling, a waxy surface, low hardness, and possible magnetism; a streak, hardness, and thin-section test can confirm it. Common in California, the Alps, New Zealand, and ophiolite belts worldwide.
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