igneous
Basalt
Basalt
AI-generated identification · may be incorrectHardness: 5.5-6 on the Mohs scale. Color: Dark gray to black, often with a brownish or reddish weathering crust. Luster: Dull to earthy. Crystal structure: Fine-grained (aphanitic), sometimes porphyritic with larger crystals (phenocrysts) of olivine or pyroxene. Specific gravity: 2.8-3.0.
- Hardness
- 5
- Luster
- Dull to earthy
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Physical properties
Hardness: 5.5-6 on the Mohs scale. Color: Dark gray to black, often with a brownish or reddish weathering crust. Luster: Dull to earthy. Crystal structure: Fine-grained (aphanitic), sometimes porphyritic with larger crystals (phenocrysts) of olivine or pyroxene. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of basaltic lava at or near the surface of a planet or moon. Typically associated with divergent plate boundaries, hotspots, and some convergent boundaries.
Uses & applications
Used in construction (crushed stone, asphalt base, concrete aggregate), railroad ballast, and sometimes as a dimension stone or in rock wool thermal insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust, forming most of the ocean floor. It is also found on the Moon, Mars, Venus, and even the asteroid Vesta.
Field identification & locations
Identify by its dark color, fine-grained texture, and high density. Often found in volcanic regions, such as Hawaii, Iceland, and the Pacific Northwest of the US. Common collector tip: Look for vesicular basalt (with holes from gas bubbles) or porphyritic basalt (with visible crystals).
