igneous
Basalt
Basalt (Aphanitic Mafic Volcanic Rock)
Hardness: 6.0; Color: Dark grey to black, sometimes greenish; Luster: Dull/earthy; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black, sometimes greenish
- Luster
- Dull/earthy
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Physical properties
Hardness: 6.0; Color: Dark grey to black, sometimes greenish; Luster: Dull/earthy; 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 at or very near the surface of a terrestrial planet or a moon. Most common rock type in the Earth's crust.
Uses & applications
Primarily used in construction for road base, concrete aggregate, railroad ballast, and dimension stone.
Geological facts
Basalt is the primary rock type of the ocean floor and is also prevalent on the Moon, Mars, and Venus. The Giant's Causeway in Northern Ireland is a famous example of columnar basalt.
Field identification & locations
Look for a heavy, dark-colored, fine-grained rock with no visible crystals to the naked eye. Often found in volcanic regions, riverbeds, and as garden landscaping.
