igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes weathering to brown or reddish-brown due to oxidation; Luster: Dull to sub-earthy; Crystal structure: Aphanitic (fine-grained), often vesicular with small gas cavities (vesicles); Specific gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Luster
- Dull to sub-earthy
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes weathering to brown or reddish-brown due to oxidation; Luster: Dull to sub-earthy; Crystal structure: Aphanitic (fine-grained), often vesicular with small gas cavities (vesicles); Specific gravity: 2.8 - 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, divergent boundaries, and flood basalt provinces.
Uses & applications
Widely used in construction for crushed stone, road base, concrete aggregate, and dimension stone, as well as in manufacturing stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also the primary volcanic rock found on the Moon and Mars.
Field identification & locations
Identified in the field by its dark color, fine-grained texture, and sometimes vesicular or frothy appearance. It forms extensive surface flows and columnar jointing structures.
