igneous
Weathered basalt (likely vesicular basalt)
Basalt, a fine-grained mafic volcanic rock; chiefly plagioclase, clinopyroxene, and iron-magnesium minerals
AI-generated identification · may be incorrectGray, dull to faintly earthy luster, fine-grained texture with small vesicles or weathering pits; typical hardness about 6 Mohs, no visible cleavage, and density roughly 2.8–3.0 g/cm³.
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Physical properties
Gray, dull to faintly earthy luster, fine-grained texture with small vesicles or weathering pits; typical hardness about 6 Mohs, no visible cleavage, and density roughly 2.8–3.0 g/cm³.
Formation & geological history
Formed when basaltic lava rapidly cooled at or near Earth’s surface, commonly in volcanic flows; its exact geological age cannot be determined from the photograph and may range from ancient to recent.
Uses & applications
Widely used as crushed aggregate, road stone, riprap, and building material; attractive polished pieces are occasionally sold as landscape or teaching specimens, but this example appears low-grade.
Geological facts
Basalt is the most abundant volcanic rock on oceanic crust and commonly forms pillow lavas, lava flows, and oceanic islands.
Field identification & locations
Identify it by its dark gray, dense fine-grained appearance, lack of visible quartz, and possible tiny gas cavities; common worldwide, especially around volcanic regions and oceanic crust. A field test with dilute acid should show little or no reaction.
