igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the surface of a planet or moon. Most basalt on Earth was formed during the Cenozoic Era, covering much of the ocean floor.
Uses & applications
Used in construction as crushed stone for road base and concrete aggregate, in the manufacture of rock wool (insulation), and as polished decorative stones or for massage therapy.
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 and Mars, forming the lunar maria (dark plains).
Field identification & locations
Identify by its heavy weight (high density), dark color, and fine-grained texture that lacks visible crystals to the naked eye. Commonly found at volcanic sites and riverbeds in volcanic regions.
