metamorphic
Greenstone, possibly serpentine or altered basalt
Serpentinite (Mg₃Si₂O₅(OH)₄) or chlorite-epidote altered basalt; identification is uncertain from the image
AI-generated identification · may be incorrectRounded green-brown specimen with dull to weakly waxy luster and mottled coloring; likely hardness ~3–6 Mohs, depending on whether it is serpentine or basalt. No visible crystals or cleavage; density likely moderate (~2.6–3.0).
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Physical properties
Rounded green-brown specimen with dull to weakly waxy luster and mottled coloring; likely hardness ~3–6 Mohs, depending on whether it is serpentine or basalt. No visible crystals or cleavage; density likely moderate (~2.6–3.0).
Formation & geological history
May form when ultramafic rock hydrates during metamorphism, producing serpentinite, or when basalt undergoes low-grade hydrothermal alteration. Such rocks range from Precambrian to modern tectonic settings.
Uses & applications
Used as ornamental stone, carvings, lapidary material, and occasionally crushed aggregate; attractive pieces may be sold as greenstone or serpentine.
Geological facts
The dark green color commonly comes from serpentine, chlorite, epidote, or iron-bearing minerals. Image-based identification cannot distinguish these reliably without hardness, streak, magnetism, or chemical tests.
Field identification & locations
Common in ophiolite belts and metamorphic terrains, including California, Vermont, New Zealand, and the Alps. Test cautiously: serpentine scratches with a steel knife, while basalt generally does not; avoid grinding unknown serpentine because some varieties may contain asbestos-form minerals.
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