igneous
Basalt (Glassy)
Basalt (Aphanitic-Glassy texture)
Hardness: 5-6 (Mohs); Color: dark gray to black; Luster: vitreous to sub-vitreous; Structure: fine-grained (aphanitic) or glassy due to rapid cooling; Fracture: conchoidal or irregular.
- Hardness
- 5-6 (Mohs)
- Color
- dark gray to black
- Luster
- vitreous to sub-vitreous
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Physical properties
Hardness: 5-6 (Mohs); Color: dark gray to black; Luster: vitreous to sub-vitreous; Structure: fine-grained (aphanitic) or glassy due to rapid cooling; Fracture: conchoidal or irregular.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. Common in oceanic crust and volcanic islands.
Uses & applications
Used extensively in construction (crushed stone), as a base material for roads, in the manufacturing of mineral wool insulation, and occasionally for lapidary work.
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon, Venus, and Mars (where it is known as lunar mare).
Field identification & locations
Identify by its dark color, heavy weight (relative to size), and lack of visible crystal grains. Found in volcanic regions or as 'river rocks' transported from volcanic sources.
