igneous
Rounded greenish river pebble, likely basalt or altered volcanic rock
Probable basalt (fine-grained mafic silicate rock), possibly epidote/chlorite-altered
AI-generated identification · may be incorrectDark olive-green to brown, dull to weakly waxy luster, rounded and water-worn; likely Mohs hardness 5–6, with no visible crystal faces or cleavage. Exact identification requires a fresh surface, streak, magnetism, and density tests.
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Physical properties
Dark olive-green to brown, dull to weakly waxy luster, rounded and water-worn; likely Mohs hardness 5–6, with no visible crystal faces or cleavage. Exact identification requires a fresh surface, streak, magnetism, and density tests.
Formation & geological history
Likely weathered from a basaltic lava flow and rounded by stream or beach transport; basalt commonly formed during the Cenozoic or older volcanic episodes. Green coloration may reflect alteration to chlorite, epidote, or other secondary minerals.
Uses & applications
Common basalt is used as aggregate, road stone, riprap, and building stone; an ordinary pebble has negligible commercial or jewelry value.
Geological facts
Basalt is rich in pyroxene and calcium-rich plagioclase, with possible olivine or alteration minerals. Its fine texture forms when lava cools relatively quickly at or near Earth’s surface.
Field identification & locations
Look for a fine, dense texture, dark streak, and occasional weak magnetism; it should not fizz with dilute hydrochloric acid unless carbonate-coated. Common worldwide, especially near volcanic regions and river gravels.
