igneous
Basalt
Basalt (Extrusive Igneous Rock)
Hardness: 5-6 Mohs. Color: Dark grey to blackish-brown. Luster: Dull to sub-metallic. Crystal Structure: Aphanitic (fine-grained). Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark grey to blackish-brown
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs. Color: Dark grey to blackish-brown. 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 magnesium-rich and iron-rich lava at or very near the Earth's surface. Common in oceanic crust and volcanic regions. Age varies by location but occurs throughout geologic history.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can be polished for decorative stone or floor tiles.
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 common on the Moon, Mars, and Venus.
Field identification & locations
Identify by its weight (denser than most common rocks), dark color, and fine-grained texture with occasional small holes (vesicles). Found in volcanic fields, riverbeds draining volcanic areas, and coastal regions.
