igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6-7 Mohs; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0; Cleavage: None, usually exhibits conchoidal fracture.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0; Cleavage: None, usually exhibits conchoidal fracture.
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 can range from Cenozoic to Precambrian in age.
Uses & applications
Basalt is used extensively in construction for aggregate, crushed stone for road bases, railroad ballast, and in the manufacturing of floor tiles and statues. High-quality basalt fibers are used in aerospace.
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 extremely common on the Moon, Mars, and Venus. Many of the 'seas' (maria) on the Moon are ancient basaltic lava flows.
Field identification & locations
Identify by its heavy weight (high density), dark color, and very fine-grained texture. It often shows small holes (vesicles) from gas bubbles. Commonly found in volcanic regions like Iceland, Hawaii, and the Pacific Northwest.
