igneous
Basalt pebble
Basalt; primarily plagioclase feldspar, pyroxene, and commonly olivine
AI-generated identification · may be incorrectFine-grained, dark gray to black, dull to faintly silky luster; hardness about 5–6 Mohs, dense, with no visible cleavage or crystals at this scale. The rounded shape indicates water or wave abrasion, and the surface appears naturally weathered or tumbled.
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Physical properties
Fine-grained, dark gray to black, dull to faintly silky luster; hardness about 5–6 Mohs, dense, with no visible cleavage or crystals at this scale. The rounded shape indicates water or wave abrasion, and the surface appears naturally weathered or tumbled.
Formation & geological history
An extrusive volcanic rock formed when mafic lava cooled rapidly at or near Earth’s surface, commonly from Cenozoic to recent volcanic activity. Exact age and source cannot be determined from the photograph.
Uses & applications
Used as crushed stone, road aggregate, railway ballast, building stone, and landscaping material; attractive polished pieces are collected as display stones.
Geological facts
Basalt is the most abundant volcanic rock in Earth’s oceanic crust and commonly forms lava flows, volcanic islands, and seafloor crust.
Field identification & locations
Identify it by its uniform dark color, fine texture, high density, and lack of visible layering or large crystals; a streak test is usually gray, and it is not strongly attracted to a magnet. Common worldwide, especially in volcanic regions and stream or beach gravels.
