metamorphic
Likely greenstone (metamorphosed basalt)
Greenschist or chlorite–epidote altered basalt; commonly composed of chlorite, epidote, actinolite, albite, and quartz
AI-generated identification · may be incorrectHardness about 5–6.5 Mohs; gray-green, fine-grained, mottled, and dull to slightly waxy; massive texture with no obvious cleavage. The rounded shape and smooth surface indicate water-worn pebble abrasion.
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Physical properties
Hardness about 5–6.5 Mohs; gray-green, fine-grained, mottled, and dull to slightly waxy; massive texture with no obvious cleavage. The rounded shape and smooth surface indicate water-worn pebble abrasion.
Formation & geological history
Formed when basaltic oceanic crust underwent low-grade regional metamorphism and hydrothermal alteration, typically during ancient tectonic activity; exact age and locality cannot be determined from the image.
Uses & applications
Used locally as landscaping stone, aggregate, and decorative carving material; attractive specimens may be polished for cabochons or display.
Geological facts
The green color generally comes from chlorite, epidote, or actinolite rather than a single mineral. “Greenstone” is a broad field term and can also refer to altered volcanic rocks or jade-like materials.
Field identification & locations
Common along beaches, rivers, and glacial deposits derived from volcanic or metamorphic bedrock. Identify by its dense fine grain, green-gray color, toughness, and lack of visible glassy or vesicular texture; laboratory testing is needed to distinguish it from serpentinite or jade.
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