igneous
Basalt
Extrusive igneous rock primarily composed of plagioclase feldspar and pyroxene
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals or volcanic glass. Specific gravity: 2.8 - 3.0.
- Hardness
- 6 on the Mohs scale
- Color
- Dark gray to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale. Color: Dark gray to black. Luster: Dull to sub-vitreous. Crystal structure: Aphanitic (fine-grained), often containing microscopic crystals or volcanic glass. Specific gravity: 2.8 - 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. Geological age ranges from Precambrian to recent volcanic activity.
Uses & applications
Used extensively in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of stone wool insulation.
Geological facts
Basalt is the most common rock type in the Earth's crust underlying the ocean basins, and it is also the predominant rock type on the surface of the Moon (forming the lunar maria) and Mars.
Field identification & locations
Identify in the field by its dark gray or black color, fine-grained texture, and sometimes vesicular structure containing gas cavities. Found worldwide in volcanic regions, oceanic islands, and large igneous provinces such as the Columbia River Basalts.
