igneous
Basalt
Extrusive Igneous Rock (Mafic)
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), often contains micro-crystals of plagioclase/pyroxene. Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black. Luster: Dull to sub-metallic. Crystal structure: Aphanitic (fine-grained), often contains micro-crystals of plagioclase/pyroxene. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or moon. Most basalt flows are from the Cenozoic era.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can be used for stone carvings or as a component in rock wool insulation.
Geological facts
Basalt is the most common rock on Earth's surface and also covers large areas of the Moon, Venus, and Mars. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt.
Field identification & locations
Identified in the field by its dark color, heavy weight (density), and fine-grained texture. Commonly found in oceanic crust, volcanic islands, and flood basalt provinces.
