igneous
Basalt
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to vitreous; Crystal structure: fine-grained (aphanitic) or glassy; Cleavage: none; Specific Gravity: 2.8–3.0
- Hardness
- 6 on Mohs scale
- Color
- dark grey to black
- Luster
- dull to vitreous
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Physical properties
Hardness: 6 on Mohs scale; Color: dark grey to black; Luster: dull to vitreous; Crystal structure: fine-grained (aphanitic) or glassy; 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 type in Earth's crust (oceanic crust).
Uses & applications
Widely used as an aggregate in construction projects, road base, concrete, and railroad ballast. Also used as dimension stone for tiles and counter tops.
Geological facts
Basalt is the most common rock type on Earth's surface and also makes up the vast majority of the lunar maria (the dark plains on the moon).
Field identification & locations
Identified by its heavy weight, dark color, and fine texture. Found in volcanic regions like the Pacific Northwest, Hawaii, and Iceland. Tools for collectors include a hand lens to see micro-crystals.
