igneous
Rounded basalt pebble
Basalt; fine-grained mafic volcanic rock, commonly dominated by plagioclase and pyroxene with minor olivine
AI-generated identification · may be incorrectDark gray, matte to slightly dull luster, fine-grained and massive; typically Mohs 5–6, with no visible cleavage or large crystals. The smooth shape indicates water abrasion or deliberate tumbling.
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Physical properties
Dark gray, matte to slightly dull luster, fine-grained and massive; typically Mohs 5–6, with no visible cleavage or large crystals. The smooth shape indicates water abrasion or deliberate tumbling.
Formation & geological history
Formed when mafic lava cooled rapidly at or near Earth’s surface, commonly during the Cenozoic or younger; exact age cannot be determined visually. It may come from a volcanic flow or a river/coastal gravel deposit.
Uses & applications
Used as aggregate, roadstone, riprap, ballast, landscaping stone, and occasionally in polished stone products. This ordinary specimen has little gem or commercial collector value.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms the seafloor, lava plateaus, and volcanic islands.
Field identification & locations
Identify it by its uniform dark gray color, fine texture, high density, and lack of visible quartz or large feldspar crystals; a streak, magnetism test, and thin-section analysis can confirm it. Common worldwide, especially volcanic regions and river beaches.
