igneous
Basalt
Basalt (Mafic Extrusive Rock)
Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to vitreous; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8–3.0.
- Hardness
- 6 on Mohs scale
- Color
- dark grey to black
- Luster
- dull to vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to vitreous; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity oceanic or continental lava (magma) rich in magnesium and iron at or very near the Earth's surface.
Uses & applications
Extensively used in construction as crushed stone for road base, railroad ballast, and concrete aggregate; also used in stone carvings and as thermal insulation (rock wool).
Geological facts
Basalt is the most common rock in Earth's crust and makes up most of the ocean floors. It is also found on other planetary bodies like the Moon, Mars, and Venus.
Field identification & locations
Identify by its heavy weight (high density), dark color, and lack of visible crystals without magnification. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
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