igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Specific Gravity: 2.9-3.1
- Hardness
- 6
- Color
- Dark grey to black
- Luster
- Dull or earthy
Identified More igneous →
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Physical properties
Hardness: 6; Color: Dark grey to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained), often containing phenocrysts; Specific Gravity: 2.9-3.1
Formation & geological history
Extrusive igneous rock formed from the rapid cooling of low-viscosity lava rich in magnesium and iron at or very near the Earth's surface. Found in oceanic crust and volcanic regions.
Uses & applications
Extensively used in construction for road base, concrete aggregate, railroad ballast, and high-quality asphalt. It is also used as a polishing stone and for stone carvings.
Geological facts
Basalt is the most common rock type on Earth's surface and also covers large areas of the Moon, Mars, and Venus. It forms the entirety of the oceanic crust.
Field identification & locations
Identify by its characteristic dark color, heavy weight (relative to size due to iron content), and lack of visible large crystal grains. Found in volcanic outcroppings and as river pebbles in volcanic regions.
