igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6.0; Color: Dark grey to black or greenish-black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None; Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black or greenish-black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black or greenish-black; 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. It is the most common volcanic rock on Earth, making up most of the ocean floor and large lava plateaus.
Uses & applications
Extensively used in construction for aggregate, road base, concrete, and railroad ballast. It is also used as a dimension stone for flooring and as a raw material for cast basalt and stone wool insulation.
Geological facts
Basalt is the primary rock type found on Mars, Venus, and the Moon. It was the material used to create the famous Giant's Causeway in Northern Ireland and the Deccan Traps in India.
Field identification & locations
Identify in the field by its heavy weight, dark color, and fine texture. It often exhibits conchoidal or irregular fracture. It is found in volcanic regions, oceanic crust, and plate boundaries.
