igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6 on Mohs scale; Color: typically dark gray to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8–3.0
- Hardness
- 6 on Mohs scale
- Color
- typically dark gray to black
- Luster
- dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6 on Mohs scale; Color: typically dark gray to black; Luster: dull to sub-metallic; Crystal structure: aphanitic (fine-grained); Specific gravity: 2.8–3.0
Formation & geological history
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
Used extensively in construction as crushed stone for road bases, concrete aggregate, and railroad ballast. Also used as floor tiles and garden landscaping.
Geological facts
Basalt is the most common rock type in Earth's crust and makes up most of the ocean floor. It is also common on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and lack of visible individual crystals without a lens. Often found in volcanic plains.
