igneous
Basalt
Mafic volcanic rock
Hardness: 6 (Mohs); Color: dark gray, black, or dark green; Luster: matte to dull; Crystal structure: fine-grained/aphanitic; Specific gravity: 2.8-3.0; often contains small phenocrysts of olivine or pyroxene.
- Hardness
- 6 (Mohs)
- Color
- dark gray, black, or dark green
- Luster
- matte to dull
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Physical properties
Hardness: 6 (Mohs); Color: dark gray, black, or dark green; Luster: matte to dull; Crystal structure: fine-grained/aphanitic; Specific gravity: 2.8-3.0; often contains small phenocrysts of olivine or pyroxene.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet or moon. It is the most common volcanic rock on Earth.
Uses & applications
Crushed stone for road base, concrete aggregate, railroad ballast, and high-tensile fiber for insulation basalt wool.
Geological facts
Basalt is the primary rock type of the ocean floor and also makes up the lunar maria on the moon. Famous formations include the Giant's Causeway in Northern Ireland.
Field identification & locations
Identify by its heavy weight relative to its size, dark color, and fine-grained texture with no visible individual crystals unless viewed under a lens. Found globally in volcanic regions.
