igneous
Likely basalt with pale mineral veins or alteration
Basalt; predominantly fine-grained plagioclase–pyroxene rock, possibly with calcite/quartz infill
AI-generated identification · may be incorrectDark gray-black, fine-grained, massive, and dull to slightly vitreous; apparent pale cream patches/veins may be calcite, quartz, or weathered alteration. Estimated hardness 5–6 for basalt, though the pale material may be softer (calcite, Mohs 3).
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Physical properties
Dark gray-black, fine-grained, massive, and dull to slightly vitreous; apparent pale cream patches/veins may be calcite, quartz, or weathered alteration. Estimated hardness 5–6 for basalt, though the pale material may be softer (calcite, Mohs 3).
Formation & geological history
Basalt forms when low-silica lava rapidly cools at or near Earth’s surface, commonly in volcanic flows and oceanic crust. The specimen’s exact age and pale vein-forming process cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, roadstone, riprap, and occasionally dimension stone; attractive polished pieces may be collected, but this example appears ordinary.
Geological facts
Basalt commonly contains microscopic crystals of plagioclase and pyroxene, sometimes with olivine. Pale patches could also represent amygdules—gas cavities later filled by secondary minerals.
Field identification & locations
Look for a dense, fine-grained dark matrix and test the pale material separately: calcite fizzes with dilute hydrochloric acid, while quartz does not and scratches glass. Common worldwide, especially volcanic regions and oceanic islands.
