igneous
Basalt
Basalt
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to submetallic; Structure: Fine-grained (aphanitic); Specific Gravity: 2.8–3.0.
- Hardness
- 6 (Mohs)
- Color
- Dark gray to black
- Luster
- Dull to submetallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark gray to black; Luster: Dull to submetallic; Structure: Fine-grained (aphanitic); Specific Gravity: 2.8–3.0.
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 a moon.
Uses & applications
Crushed stone for road base, concrete aggregate, railroad ballast, and floor tiles; also used as a raw material for stone wool insulation.
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight compared to other similar-sized rocks, and lack of visible crystals. Commonly found in volcanic regions and riverbeds.
