igneous
Basalt Pebble
Extrusive igneous rock
Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained (aphanitic) crystal structure, dull to sub-vitreous luster, high specific gravity (2.8-3.0)
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black color, fine-grained (aphanitic) crystal structure, dull to sub-vitreous luster, high specific gravity (2.8-3.0)
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the surface of a planet or moon
Uses & applications
Used in construction, as aggregate in concrete, road base, and crushed stone for railway ballast
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins and also makes up extensive volcanic provinces on the continents
Field identification & locations
Found abundantly in riverbeds, beaches, and volcanic regions worldwide; easily identified by its dark, dense, fine-grained appearance and smooth rounded shape from water tumbling
