igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); 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 is less than 200 million years old.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and high-quality stone carvings or architectural tiles.
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus.
Field identification & locations
Identify by its heavy weight (high density), dark color, and lack of visible crystals. It often forms spectacular columnar jointing in the field. Common in volcanic regions like Hawaii, Iceland, and the Pacific Northwest.
