igneous
Basalt with a light-colored mineral vein or alteration patch
Fine-grained basalt, likely containing plagioclase and/or calcite–zeolite infill
AI-generated identification · may be incorrectDark gray, rounded, fine-grained volcanic rock with a dull to slightly waxy luster; hardness about 5–6, generally massive with no visible cleavage. The pale patch may be feldspar-rich material, calcite, or zeolite filling a fracture or vesicle; exact identification requires testing.
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Physical properties
Dark gray, rounded, fine-grained volcanic rock with a dull to slightly waxy luster; hardness about 5–6, generally massive with no visible cleavage. The pale patch may be feldspar-rich material, calcite, or zeolite filling a fracture or vesicle; exact identification requires testing.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava cools rapidly at or near Earth’s surface, commonly in oceanic crust and volcanic fields. The pale material likely formed later from mineral-rich fluids; the specimen’s precise age and locality cannot be determined from the image.
Uses & applications
Used widely as crushed aggregate, road stone, riprap, and occasionally building stone; attractive polished pieces are collected. The specimen has modest value unless its vein minerals or locality are distinctive.
Geological facts
The rounded shape suggests stream or beach abrasion. Basalt commonly contains microscopic plagioclase and pyroxene crystals, while fractures may host calcite, quartz, or zeolites.
Field identification & locations
Identify by its heavy, fine-grained dark matrix and lack of obvious individual crystals; a streak, acid, hardness, and close-up test can distinguish calcite from feldspar or zeolite. Common worldwide, especially volcanic regions and ocean beaches.
