igneous
Crushed basalt and andesite aggregate
Basalt–andesite volcanic rock; primarily plagioclase feldspar, pyroxene, and minor olivine or amphibole
AI-generated identification · may be incorrectDark gray to black, commonly fine-grained and massive, with occasional reddish weathering; dull to faintly glassy luster, Mohs hardness about 5–6, no consistent cleavage, and specific gravity roughly 2.7–3.0.
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Physical properties
Dark gray to black, commonly fine-grained and massive, with occasional reddish weathering; dull to faintly glassy luster, Mohs hardness about 5–6, no consistent cleavage, and specific gravity roughly 2.7–3.0.
Formation & geological history
Formed from rapidly cooled lava, generally in volcanic flows during the Cenozoic or older eras; the pieces shown are mechanically crushed and screened aggregate rather than natural rounded gravel.
Uses & applications
Widely used for road base, drainage, railway ballast, landscaping, concrete aggregate, and asphalt; generally has little jewelry or collector value.
Geological facts
Basalt is the most abundant volcanic rock on Earth and commonly forms oceanic crust. The lighter, more silica-rich pieces may be andesite or weathered basalt.
Field identification & locations
Identify it by its dark color, dense fine-grained texture, angular crushed surfaces, and lack of visible large crystals; common near volcanic regions and aggregate quarries worldwide.
