metamorphic
Weathered ultramafic rock, likely serpentinite
Serpentinite; chiefly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), with magnetite and possible olivine/pyroxene remnants
AI-generated identification · may be incorrectTypically dark green, olive, brown, or yellow-brown with waxy to dull luster; hardness about 2.5–4, nonfoliated to weakly foliated, and commonly mottled or veined. This specimen’s rusty weathering and dark granular patches are consistent with serpentinite, though a photo cannot confirm composition.
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Physical properties
Typically dark green, olive, brown, or yellow-brown with waxy to dull luster; hardness about 2.5–4, nonfoliated to weakly foliated, and commonly mottled or veined. This specimen’s rusty weathering and dark granular patches are consistent with serpentinite, though a photo cannot confirm composition.
Formation & geological history
Forms when mantle peridotite is hydrated and metamorphosed, commonly along oceanic crust and tectonic plate boundaries; ages vary from Precambrian to Cenozoic depending on the host terrane.
Uses & applications
Used as decorative stone, carving material, aggregate, and historically for architectural facing; attractive polished pieces are collected, though fibrous asbestos-bearing varieties require caution.
Geological facts
Iron oxidation produces the brown, gold, and red surface colors, while magnetite may make the rock weakly magnetic. Associated minerals can include chromite, talc, carbonate, and tremolite.
Field identification & locations
Look for green-black mottling, waxy surfaces, slickensides, and possible magnetism; common in ophiolites and major fault zones. Confirm with hardness, streak, magnet test, and ideally thin-section or chemical analysis.
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