igneous
Basalt
Basalt (Mafic Extrusive)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/Sub-metallic; Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull/Sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull/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. Most common rock on Earth's crust.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. Also used in high-temp insulation (rock wool) and as decorative garden stone.
Geological facts
Basalt makes up most of the ocean floor on Earth and is also found on the Moon, Mars, and Venus. It often forms striking geometric columns like those at Giant's Causeway.
Field identification & locations
Identify in the field by its high density, dark color, and lack of visible crystals to the naked eye. Often weathered to a reddish-brown crust. Look for it in volcanic regions or riverbeds.
