igneous
Basalt
Extrusive mafic rock
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often weathering to brown/green; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black, often weathering to brown/green
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often weathering to brown/green; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained) to porphyritic; 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 a moon. Most common rock in Earth's crust (oceanic).
Uses & applications
Extensively used in construction as aggregate for roads, railroad ballast, and concrete; also used as a dimension stone for floor tiles and monument sculptures.
Geological facts
Basalt is the most common rock type on the surface of the Moon and Mars. It provides the dark coloring of the lunar maria.
Field identification & locations
Identify by its heavy weight (high density), fine grain size where individual crystals are not visible to the naked eye, and dark color. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
