igneous
Basalt
Mafic Igneous Rock (Basalt)
Hardness: 6 (Mohs); Color: dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; Specific gravity: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- dark grey to black
- Luster
- dull to earthy
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Physical properties
Hardness: 6 (Mohs); Color: dark grey to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) or porphyritic; 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 arcs.
Uses & applications
Mainly used in construction as aggregate, road base, railroad ballast, and sometimes in stone carving or as high-strength insulation (rock wool).
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its dark color, high density, and lack of visible large quartz crystals. Commonly found in coastal areas or near volcanic hotspots like Hawaii or the Pacific Northwest.
