igneous
Weathered basalt pebble
Basalt, a fine-grained mafic volcanic rock composed mainly of plagioclase feldspar and pyroxene, commonly with olivine
AI-generated identification · may be incorrectDark gray-green, dull to slightly earthy luster, fine-grained and rounded by abrasion; hardness about 6 Mohs, with no obvious cleavage and typically high density (approximately 2.8–3.0). The pitted surface may reflect vesicles, weathering, or mineral alteration.
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Physical properties
Dark gray-green, dull to slightly earthy luster, fine-grained and rounded by abrasion; hardness about 6 Mohs, with no obvious cleavage and typically high density (approximately 2.8–3.0). The pitted surface may reflect vesicles, weathering, or mineral alteration.
Formation & geological history
Formed when iron- and magnesium-rich lava cooled rapidly at or near Earth’s surface, generally in Cenozoic or older volcanic terrains; the specimen was later rounded by stream, beach, or glacial transport.
Uses & applications
Used extensively as crushed aggregate, road stone, riprap, railroad ballast, and occasionally as landscaping stone or a carving/tumbling material; this small weathered piece has little jewelry value.
Geological facts
Basalt is Earth’s most abundant volcanic rock and forms much of the oceanic crust, including seafloor at mid-ocean ridges and large volcanic plateaus.
Field identification & locations
Identify it by its dense, dark, fine-grained texture, lack of visible large crystals, and weak attraction to a magnet if iron-rich; common in volcanic regions, river gravels, and beaches. A fresh broken surface is more diagnostic than the weathered exterior.
