igneous
Weathered basalt pebble
Basalt, a fine-grained mafic volcanic rock; likely olivine- and pyroxene-bearing
AI-generated identification · may be incorrectTypically Mohs 5–6, dark gray to brown with dull-to-submetallic luster; compact, fine-grained, and lacking visible cleavage. The pale patches are likely weathering rinds, alteration minerals, or adhered sediment rather than metallic material.
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Physical properties
Typically Mohs 5–6, dark gray to brown with dull-to-submetallic luster; compact, fine-grained, and lacking visible cleavage. The pale patches are likely weathering rinds, alteration minerals, or adhered sediment rather than metallic material.
Formation & geological history
Formed when mafic lava rapidly cooled at or near Earth’s surface, generally in the Cenozoic or older depending on locality; rounded shape indicates stream, beach, or glacial transport and abrasion.
Uses & applications
Commonly used as crushed aggregate, road stone, ballast, riprap, and occasionally dimension stone; this unremarkable specimen has little jewelry use.
Geological facts
Basalt is the most abundant volcanic rock on Earth and forms much of oceanic crust. Its iron- and magnesium-rich minerals commonly weather to brown oxides and clay minerals.
Field identification & locations
Identify by its high density, dark fine-grained texture, and inability to scratch glass reliably; a streak test is usually gray-brown. Common worldwide, especially volcanic regions, river gravels, beaches, and glacial deposits.
