igneous
Possible basalt pebble
Basalt; fine-grained mafic volcanic rock, chiefly plagioclase and pyroxene
AI-generated identification · may be incorrectDark gray-green, rounded and apparently weathered, with a dull to faintly granular luster and tiny pale mineral grains. Typically hardness 5–6 Mohs, massive with no cleavage, and specific gravity about 2.8–3.0; the image alone cannot confirm composition.
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Physical properties
Dark gray-green, rounded and apparently weathered, with a dull to faintly granular luster and tiny pale mineral grains. Typically hardness 5–6 Mohs, massive with no cleavage, and specific gravity about 2.8–3.0; the image alone cannot confirm composition.
Formation & geological history
Basalt forms when iron- and magnesium-rich lava rapidly cools at or near Earth’s surface, commonly in oceanic crust, lava flows, and volcanic islands. Most specimens are geologically young relative to continental rocks, though basalt occurs from Archean to present.
Uses & applications
Used as crushed aggregate, road stone, riprap, and occasionally building or landscaping stone; ordinary pebbles have little jewelry value.
Geological facts
Its rounded shape indicates transport and abrasion, likely in a river, beach, or glacial deposit. The small bright flecks may be feldspar, pyroxene, or weathering minerals.
Field identification & locations
Test for a dark streak, high density, and lack of visible layering; a steel file may scratch it, while it should not fizz with dilute hydrochloric acid. Common worldwide, especially volcanic regions and river gravels.
