igneous
Basalt Outcropping
Aphanitic Mafic Igneous Rock
Hardness: 5-6 Mohs. Color: Dark gray to black, weathering to brown or reddish-brown. Luster: Dull to sub-metallic. Structure: Fine-grained (aphanitic) or vesicular. Specific Gravity: 2.9-3.1.
- Hardness
- 5-6 Mohs
- Color
- Dark gray to black, weathering to brown or reddish-brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 Mohs. Color: Dark gray to black, weathering to brown or reddish-brown. Luster: Dull to sub-metallic. Structure: Fine-grained (aphanitic) or vesicular. Specific Gravity: 2.9-3.1.
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. Common in volcanic arcs and oceanic hotspots.
Uses & applications
Used extensively in construction as aggregate for roads, railroad ballast, and in concrete. High-quality specimens are used for stone carving and as thermal insulators (rock wool).
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identified in the field by its dark color, heavy weight (density), and fine-grained texture. It often exhibits columnar jointing in large flows. Commonly found in volcanic regions.
