metamorphic
Greenstone (likely altered basalt)
Greenschist-facies metabasalt; commonly composed of chlorite, actinolite, epidote, and albite
AI-generated identification · may be incorrectMuted green-gray, fine-grained, and rounded/polished; likely Mohs 5–6, with a dull to slightly waxy luster. Exact mineralogy and hardness cannot be confirmed from the image.
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Physical properties
Muted green-gray, fine-grained, and rounded/polished; likely Mohs 5–6, with a dull to slightly waxy luster. Exact mineralogy and hardness cannot be confirmed from the image.
Formation & geological history
Typically forms when basalt is altered by low-grade regional metamorphism and hydrothermal fluids. Such rocks occur in ancient metamorphic belts of many geological ages.
Uses & applications
Used as an ornamental or carving stone and collected as a polished specimen; some greenstone has historically been fashioned into tools and beads.
Geological facts
“Greenstone” is a field term for green-hued, altered mafic rock, not a single precise mineral or composition.
Field identification & locations
Look for a dense, fine-grained green rock, often with chlorite- or epidote-related color; confirm by examining a fresh surface and testing hardness. Found in metamorphic belts worldwide.
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