igneous
Basalt
Basalt
Hardness: 6.0 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark gray to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0 (Mohs scale); Color: Dark gray to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; 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. Most basalt on Earth was formed over the last 200 million years.
Uses & applications
Extensively used in construction, specifically as road base, railroad ballast, and aggregate in concrete. High-quality specimens are used in architectural stone and stone wool insulation.
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also common on the Moon, Mars, and Venus.
Field identification & locations
Identified in the field by its dark color, heavy weight (relative to same-sized rocks), and very fine grains. Commonly found in volcanic regions, oceanic crust, and plateaus created by flood basalts.
