igneous
Basalt Pebble
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale, dark gray to black color, aphanitic (fine-grained) crystal structure, subconchoidal fracture, and specific gravity around 2.8 - 3.0.
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Physical properties
Hardness of 6 on the Mohs scale, dark gray to black color, aphanitic (fine-grained) crystal structure, subconchoidal fracture, and specific gravity around 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 crushed aggregate for road bases, railroad ballast, and in the production of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's ocean basins and forms prominent geological features like the Giant's Causeway in Northern Ireland.
Field identification & locations
Found worldwide in volcanic regions, riverbeds, and beaches where wave action has tumbled and smoothed the rock into a pebble.
