igneous
Basalt
Mafic Igneous Rock (primarily Plagioclase and Pyroxene)
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8–3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface of a planet or moon. Most basalt on Earth was formed within the last 200 million years.
Uses & applications
Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate; also used for stone carvings and floor tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the ocean floor. Large areas of the Moon and Mars are also covered in basaltic lava plains.
Field identification & locations
Identify by its dark color, heavy weight compared to common stones, and fine-grained texture. Commonly found in volcanic regions, oceanic crust, and plate tectonic boundaries.
