igneous
Weathered mafic rock, likely basalt or greenstone
Fine-grained basaltic rock; possibly altered basalt (metabasalt/greenstone)
AI-generated identification · may be incorrectDark gray-green, fine-grained, dull to weakly silky luster, with weathered pits and mottled pale mineral patches. Basalt typically has Mohs hardness 6–7, no obvious cleavage, and specific gravity around 2.8–3.1; exact identification requires a fresh surface and tests.
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Physical properties
Dark gray-green, fine-grained, dull to weakly silky luster, with weathered pits and mottled pale mineral patches. Basalt typically has Mohs hardness 6–7, no obvious cleavage, and specific gravity around 2.8–3.1; exact identification requires a fresh surface and tests.
Formation & geological history
Likely formed from rapidly cooled basaltic lava, or from low-grade metamorphism and alteration of basalt. Basalt ranges from Precambrian to modern, while greenstone commonly forms in ancient oceanic crust and volcanic belts.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally dimension stone; attractive polished pieces may be collected but are usually low-value.
Geological facts
The green color may reflect chlorite, epidote, actinolite, or serpentine replacing original volcanic minerals. The rounded shape and surface cavities indicate prolonged stream or beach abrasion and weathering.
Field identification & locations
Common in volcanic terrains, oceanic crust, and glacial or river gravels. Look for a dark fine-grained interior, high density, lack of fizz in dilute acid, and possible weak attraction to a magnet; a streak, hardness, and thin-section test would refine the identification.
