metamorphic
Serpentinite pebble
Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), commonly with magnetite, chromite, and carbonate
AI-generated identification · may be incorrectDark green, brown, and black mottling with waxy to greasy luster; typically massive and fine-grained, Mohs hardness about 2.5–4, with no obvious cleavage and specific gravity around 2.5–2.6. The rounded shape indicates water abrasion.
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Physical properties
Dark green, brown, and black mottling with waxy to greasy luster; typically massive and fine-grained, Mohs hardness about 2.5–4, with no obvious cleavage and specific gravity around 2.5–2.6. The rounded shape indicates water abrasion.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite undergo low-temperature hydration and metamorphism, commonly in oceanic crust and subduction zones. Serpentinization ranges from Paleozoic to modern geological settings.
Uses & applications
Used as decorative stone, carving material, architectural facing, and historically as a source of asbestos-bearing serpentine; attractive polished pieces are collected but are usually modestly priced.
Geological facts
Often contains magnetite, making some specimens weakly magnetic. The green color and slick, smooth texture result from serpentine minerals replacing olivine and pyroxene.
Field identification & locations
Identify by its mottled green-black color, waxy surface, low hardness, and occasional magnetism; common in California, Vermont, Italy, New Zealand, and ophiolite belts worldwide. Avoid cutting or sanding unknown specimens because some serpentinite contains fibrous chrysotile asbestos.
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