igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6 (Mohs); Color: dark gray to black; Luster: dull to earthy; Structure: fine-grained (aphanitic); Specific Gravity: 2.8–3.0.
- Hardness
- 6 (Mohs)
- Color
- dark gray to black
- Luster
- dull to earthy
Identified More igneous →
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Physical properties
Hardness: 6 (Mohs); Color: dark gray to black; Luster: dull to earthy; 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 at or very near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and high-quality floor tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the surface of the Moon and Mars.
Field identification & locations
Identify by its heavy weight (density) and dark, fine-grained surface that often lacks visible crystals to the naked eye. Found worldwide in volcanic fields.
