igneous
Basalt
Basalt (Mafic igneous rock)
Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 6 (Mohs scale)
- Color
- Black to dark gray
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 (Mohs scale); Color: Black to dark gray; Luster: Dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. Common in oceanic crust and volcanic regions.
Uses & applications
Used extensively in construction as aggregate for roads and concrete, in railroad ballast, and sometimes carved for decorative sculptures or tiles.
Geological facts
Basalt is the most common rock on Earth's surface, making up most of the ocean floor and major volcanic islands like Hawaii and Iceland.
Field identification & locations
Identified in the field by its dark color, high density, and fine-grained texture. It often shows vesiculation (small holes) or columnar jointing in large outcrops.
