igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Microcrystalline (aphanitic); Cleavage: None; 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: Microcrystalline (aphanitic); 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 moon. Typically found in volcanic fields and oceanic crust.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and high-quality asphalt. It is also used as a raw material for stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also found on the Moon and Mars, forming the dark 'maria' plains visible from Earth.
Field identification & locations
Identified in the field by its dark color, heavy weight (relative to size), and fine-grained texture. It often breaks with sharp edges and can sometimes exhibit a vesicular (holed) or columnar structure.
