igneous
Basalt
Basalt
Hardness: 6.0; Color: dark grey to black; Luster: dull to submetallic; Crystal structure: aphanitic (fine-grained); Cleavage: none; Specific gravity: 2.8-3.0
- Hardness
- 6
- Color
- dark grey to black
- Luster
- dull to submetallic
Identified More igneous →
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Physical properties
Hardness: 6.0; Color: dark grey to black; Luster: dull to submetallic; Crystal structure: aphanitic (fine-grained); Cleavage: none; Specific gravity: 2.8-3.0
Formation & geological history
Formed through the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. Most basalt on Earth is of Cenozoic to Archean age.
Uses & applications
Used widely in construction as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality specimens are used in stone carving and architecture.
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, where it forms the lunar maria.
Field identification & locations
Identify by its dark color, heavy weight, and fine-grained texture. It often shows vesicles (small holes) or a smooth, water-worn surface if found in rivers. Found globally in volcanic regions.
