igneous
Veined basalt pebble
Basalt, chiefly plagioclase and pyroxene, cut by pale mineral veins (likely calcite or quartz)
AI-generated identification · may be incorrectDark gray, fine-grained, rounded and naturally weathered; dull to faintly silky luster, no visible crystals or cleavage. Hardness is approximately 5–6 for basalt; veins may be softer calcite (Mohs 3) or harder quartz (Mohs 7).
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Physical properties
Dark gray, fine-grained, rounded and naturally weathered; dull to faintly silky luster, no visible crystals or cleavage. Hardness is approximately 5–6 for basalt; veins may be softer calcite (Mohs 3) or harder quartz (Mohs 7).
Formation & geological history
Basalt formed when low-silica lava cooled rapidly at or near Earth’s surface, commonly in volcanic fields or oceanic crust. The white veins formed later when mineral-rich fluids filled fractures; the rock may be millions to hundreds of millions of years old depending on its source.
Uses & applications
Used as aggregate, road stone, riprap, and building stone; attractive veined pieces are collected or used as decorative cobbles. This small specimen has modest commercial value.
Geological facts
The pale network is a secondary mineral feature rather than the basalt’s original texture. Effervescence with dilute hydrochloric acid would suggest calcite; no reaction and a glass-scratching vein would favor quartz.
Field identification & locations
Common near volcanic terrains, river gravels, and beaches. Identify it by its dense dark fine grain, heavy feel, and contrasting fracture-filling veins; a streak test and acid test can help determine the vein mineral.
