igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs scale); Color: Dark gray, dark brown, to black; Luster: Sub-vitreous to dull; Crystal structure: Aphanitic (fine-grained), microcrystalline; Cleavage: None (conchoidal to irregular fracture); Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark gray, dark brown, to black
- Luster
- Sub-vitreous to dull
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark gray, dark brown, to black; Luster: Sub-vitreous to dull; Crystal structure: Aphanitic (fine-grained), microcrystalline; Cleavage: None (conchoidal to irregular fracture); Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling and crystallization of basaltic lava at or near the Earth's surface. Commonly associated with oceanic crust, mid-ocean ridges, volcanic island arcs, and continental flood basalts.
Uses & applications
Extensively used as crushed stone in construction, road base, concrete aggregate, railway ballast, and dimension stone for pavers or statues.
Geological facts
Basalt is the most common rock type in the Earth's crust, covering most of the ocean floors. It is also extremely common on terrestrial planetary bodies like the Moon (lunar maria) and Mars.
Field identification & locations
Identified in the field by its dense, fine-grained texture and dark gray to black color. Widely found worldwide in volcanic regions such as Hawaii, Iceland, and the Pacific Northwest.
