metamorphic
Likely greenstone (serpentinized ultramafic rock)
Serpentinite, dominated by serpentine-group minerals (chrysotile/lizardite/antigorite), possibly with chlorite or epidote
AI-generated identification · may be incorrectDark green, mottled and fine-grained with a waxy to dull luster; typically Mohs 2.5–4, massive, with no obvious cleavage and specific gravity about 2.5–2.7. The rounded surface and green veining are consistent with weathered serpentinite, though the image is not diagnostic.
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Physical properties
Dark green, mottled and fine-grained with a waxy to dull luster; typically Mohs 2.5–4, massive, with no obvious cleavage and specific gravity about 2.5–2.7. The rounded surface and green veining are consistent with weathered serpentinite, though the image is not diagnostic.
Formation & geological history
Forms when mantle-derived peridotite is hydrated and metamorphosed during ocean-floor alteration or subduction; ages vary widely, commonly Precambrian to Mesozoic. The specimen appears water-worn or naturally weathered.
Uses & applications
Used as decorative stone, carvings, aggregate, and historically as a building stone; attractive pieces may be polished, but fibrous varieties should not be cut or abraded because some contain asbestos-form serpentine.
Geological facts
Greenstone is a broad informal term and can also refer to altered basalt or other green rocks; chemical or thin-section testing is needed for certainty.
Field identification & locations
Look for low hardness, greasy/waxy green surfaces, dark veining, and a relatively light feel; common in ophiolites and metamorphic belts, including California, Italy, New Zealand, and Canada.
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