igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often vesicular; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained), often vesicular; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the Earth's surface, common in volcanic environments and oceanic crusts.
Uses & applications
Used extensively in construction, road base, aggregate, railroad ballast, and in the manufacturing of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust, forming most of the oceanic crust and making up massive volcanic formations like the Columbia River Basalt Group and the Giant's Causeway in Ireland.
Field identification & locations
Identify by its dark gray or black color, heavy feel, and very fine-grained texture. Commonly found globally in volcanic regions and oceanic islands like Hawaii and Iceland.
