igneous
Basalt
Extrusive igneous rock
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitellus; Crystal structure: Aphanitic (fine-grained), glassy or vesicular; Specific gravity: 2.8-3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitellus
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitellus; Crystal structure: Aphanitic (fine-grained), glassy or vesicular; Specific gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in iron and magnesium exposed at or very near the Earth's surface, typically associated with volcanic activity and oceanic crust formation.
Uses & applications
Used in construction as crushed stone for road base, concrete aggregate, asphalt pavement, and railroad ballast, as well as in the production of rock wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor and also forming massive volcanic structures on other terrestrial planets like Mars and Venus, such as Olympus Mons.
Field identification & locations
Easily identified by its dark grey to black color, heavy feel relative to its size, and fine-grained texture. Commonly found in volcanic regions, oceanic islands, and ancient lava flows worldwide.
