igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Aphanitic (fine-grained), dull to sub-vitreous. Crystal structure: Microcrystalline, generally too small to see with the naked eye. Specific gravity: 2.8 to 3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Aphanitic (fine-grained), dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Aphanitic (fine-grained), dull to sub-vitreous. Crystal structure: Microcrystalline, generally too small to see with the naked eye. Specific gravity: 2.8 to 3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity lava rich in magnesium and iron exposed at or very near the surface of a planet or moon. Formed globally throughout geological time, from the Precambrian to active volcanic eruptions today.
Uses & applications
Used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the manufacturing of stone wool insulation and tiles.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also the most common volcanic rock on the terrestrial planets, including the Moon (forming the lunar maria) and Mars.
Field identification & locations
Identify in the field by its dark color, heavy feel relative to its size, and fine-grained texture. Commonly found in volcanic regions, oceanic islands, and flood basalt provinces worldwide.
