igneous
Basalt
Basalt (containing mainly Plagioclase feldspar and Pyroxene)
Hardness: 6 on Mohs scale; Color: typically dark gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) due to rapid cooling; Cleavage: none; Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on Mohs scale
- Color
- typically dark gray to black
- Luster
- dull to earthy
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Physical properties
Hardness: 6 on Mohs scale; Color: typically dark gray to black; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic) due to rapid cooling; 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 found in oceanic crust and volcanic hotspots across all geological ages.
Uses & applications
Extensively used in construction for aggregate in concrete and asphalt, road base, railroad ballast, and sometimes as a dimension stone for floor tiles or monument bases.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also covers large areas of the Moon, Mars, and Venus, manifesting as 'maria' (dark plains) on the moon.
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and fine-grained texture which lacks visible crystals to the naked eye. Commonly found in volcanic regions, near oceanic ridges, or as glacial erratics in some regions.
