igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs scale); Color: Dark grey to black, sometimes greenish when weathered; Luster: Dull to sub-metallic when wet; Structure: Aphanitic (fine-grained), often vesicular; Specific Gravity: 2.8-3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black, sometimes greenish when weathered
- Luster
- Dull to sub-metallic when wet
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black, sometimes greenish when weathered; Luster: Dull to sub-metallic when wet; Structure: Aphanitic (fine-grained), often vesicular; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (basaltic magma) exposed at or very near the Earth's surface.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and as a dimension stone for floor tiles and monuments.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
