igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None/conchoidal fracture; Specific Gravity: 2.8–3.0
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0; Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Cleavage: None/conchoidal fracture; 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. Common in oceanic crust and lava flows.
Uses & applications
Extensively used in construction, especially as road base, railroad ballast, concrete aggregate, and as a raw material for stone wool insulation. Used occasionally in decorative flagstones.
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
Identified by its heavy weight (high density), dark color, and very fine-grained texture. Commonly found in volcanic regions like Iceland, Hawaii, and the Pacific Northwest.
