igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 (Mohs); Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: fine-grained (aphanitic) or porphyritic; 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: fine-grained (aphanitic) or porphyritic; Cleavage: none; 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. It can be of various ages from Archean to modern day.
Uses & applications
Used extensively in construction as aggregate for roads, railroad ballast, and in concrete; also used as a carving stone for monuments and in some industrial melting processes.
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also a primary component of the Moon's lunar maria and parts of Mars and Venus.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows a weathered brown or red exterior. Common in volcanic regions like the Pacific Northwest, Iceland, and Hawaii.
