igneous
Basalt
Extrusive mafic igneous rock
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6-7 Mohs
- Color
- dark grey to black
- Luster
- dull to sub-metallic
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Physical properties
Hardness: 6-7 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.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for stone carving and as a heat sink.
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.
Field identification & locations
Identify by its dark color, heavy weight, and fine-grained texture. Often found in volcanic regions, oceanic islands, and mid-ocean ridges.
