igneous
Basalt pebble
Basalt; fine-grained mafic volcanic rock, typically plagioclase + pyroxene ± olivine
AI-generated identification · may be incorrectDark gray-brown, fine-grained, dull to slightly earthy luster, with numerous small vesicles; hardness about 5–6 Mohs and specific gravity roughly 2.8–3.0. The smoothly rounded, curved form indicates water abrasion or natural weathering; the holes are gas bubbles (vesicles).
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Physical properties
Dark gray-brown, fine-grained, dull to slightly earthy luster, with numerous small vesicles; hardness about 5–6 Mohs and specific gravity roughly 2.8–3.0. The smoothly rounded, curved form indicates water abrasion or natural weathering; the holes are gas bubbles (vesicles).
Formation & geological history
Formed when low-silica basaltic lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or older volcanic episodes; the exact age cannot be determined visually. Its rounded shape likely developed in a river, beach, or wave environment.
Uses & applications
Used as aggregate, road stone, riprap, and occasionally decorative stone; this small weathered specimen has little jewelry value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of the oceanic crust. Vesicular basalt can resemble scoria, but this piece is unusually dense and heavily weathered.
Field identification & locations
Identify it by its dark color, fine texture, heaviness, and lack of visible large crystals; a streak test is usually gray, and a magnet may show weak attraction if iron minerals are abundant. Common sources include volcanic islands, ocean beaches, river gravels, and continental lava fields.
