igneous
Basalt
Basalt (Igneous Volcanic)
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Cleavage: None (conchoidal fracture).
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Cleavage: None (conchoidal fracture).
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 terrestrial basalt was formed during the Cenozoic era, though occurrences span earth's history.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and concrete. Also used for high-quality floor tiles and as a raw material for stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture. To find it, look in volcanic regions, oceanic islands (like Hawaii), and mid-ocean ridges.
