igneous
Weathered dark volcanic rock, likely basalt
Basalt; predominantly plagioclase feldspar and pyroxene, with possible olivine and secondary alteration minerals
AI-generated identification · may be incorrectDark gray, fine-grained, dull to weakly waxy luster, massive texture, and no obvious cleavage; hardness is about 5–6 Mohs and specific gravity roughly 2.8–3.1. White surface patches appear to be weathering or mineral crusts, while the rounded shape suggests abrasion or transport.
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Physical properties
Dark gray, fine-grained, dull to weakly waxy luster, massive texture, and no obvious cleavage; hardness is about 5–6 Mohs and specific gravity roughly 2.8–3.1. White surface patches appear to be weathering or mineral crusts, while the rounded shape suggests abrasion or transport.
Formation & geological history
Basalt forms when low-silica magma rapidly cools at or near Earth’s surface, commonly in lava flows, oceanic crust, and volcanic fields. Its exact age cannot be determined from the image; it may range from recent to billions of years old.
Uses & applications
Basalt is widely used as crushed aggregate, roadstone, riprap, building stone, and sometimes dimension stone. This ordinary weathered specimen has little jewelry value but may interest rock collectors.
Geological facts
Basalt commonly contains microscopic crystals because of rapid cooling; larger crystals may indicate slower cooling or later alteration. Vesicles, if present, can be filled with zeolite, calcite, or quartz.
Field identification & locations
Identify it by its dark color, heavy feel, fine grain, and resistance to scratching; a steel file usually scratches it only weakly. Common sources include volcanic regions, ocean beaches, river gravels, and quarry sites.
