igneous
Basalt
Extrusive Igneous Rock
Hardness of 6 on the Mohs scale; dark gray to black in color; dull to sub-aphanitic luster; fine-grained (aphanitic) crystal structure composed primarily of plagioclase feldspar and pyroxene; specific gravity ranges from 2.8 to 3.0.
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Physical properties
Hardness of 6 on the Mohs scale; dark gray to black in color; dull to sub-aphanitic luster; fine-grained (aphanitic) crystal structure composed primarily of plagioclase feldspar and pyroxene; specific gravity ranges from 2.8 to 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the Earth's surface, commonly associated with volcanic hotspots and divergent plate boundaries.
Uses & applications
Widely used in construction as crushed stone for road bases, concrete aggregate, and railroad ballast, as well as in manufacturing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the world's oceans. Similar dark volcanic rocks also cover extensive regions of the Moon's maria and the surface of Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight, and fine-grained texture where individual minerals are difficult to see without a hand lens. Found worldwide in volcanic regions.
