metamorphic
Serpentine with quartz or calcite vein
Serpentinite; mainly serpentine-group minerals (Mg₃Si₂O₅(OH)₄), with a pale quartz/calcite vein
AI-generated identification · may be incorrectDark green to black, mottled and waxy to subvitreous, with a contrasting cream vein and curved foliation. Serpentine is typically Mohs 2.5–4, has poor cleavage, fine-grained fibrous crystal structure, and specific gravity about 2.5–2.6; exact hardness and vein mineral require testing.
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Physical properties
Dark green to black, mottled and waxy to subvitreous, with a contrasting cream vein and curved foliation. Serpentine is typically Mohs 2.5–4, has poor cleavage, fine-grained fibrous crystal structure, and specific gravity about 2.5–2.6; exact hardness and vein mineral require testing.
Formation & geological history
Forms when ultramafic mantle rocks such as peridotite hydrate during metamorphism, commonly along oceanic crust and tectonic faults. The specimen’s age cannot be determined from the photograph; serpentinization may occur at various geological ages.
Uses & applications
Used as ornamental stone, carvings, countertops, and historically as a decorative substitute for jade; attractive small specimens are collected. Avoid cutting or generating dust until asbestos-form serpentine is excluded.
Geological facts
The pale band is probably a later fracture-filling vein of calcite or quartz, producing the distinctive brecciated appearance. Serpentinite is often associated with chromite, magnetite, and occasionally talc or asbestos minerals.
Field identification & locations
Likely identification: green-black serpentinite pebble with a pale vein. Test hardness: calcite scratches easily and fizzes in dilute acid, while quartz does not; serpentine commonly scratches with a steel knife but not glass. Common in Alpine-type belts, California, Italy, New Zealand, and Japan.
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