igneous
Basalt
Extrusive Igneous Rock
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained), sometimes porphyritic or vesicular; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on the Mohs scale
- Color
- Dark grey to black
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on the Mohs scale; Color: Dark grey to black; Luster: Dull to sub-vitreous; Crystal Structure: Aphanitic (fine-grained), sometimes porphyritic or vesicular; Specific Gravity: 2.8 - 3.0
Formation & geological history
Formed from the rapid cooling of low-viscosity, magnesium- and iron-rich lava exposed at or very near the surface of a planet or moon. Geological age ranges widely from recent volcanic activity to Precambrian times.
Uses & applications
Commonly used in construction as crushed stone for road bases, concrete aggregate, railroad ballast, and in the production of basalt fiber.
Geological facts
Basalt is the most common rock type in the Earth's crust, underlying more than 90% of all volcanic areas. It is also the primary rock type making up the dark regions of the Moon's surface, known as the lunar maria.
Field identification & locations
Easily identified by its dark grey to black color, fine-grained texture, and dense, heavy feel. Found globally in oceanic crusts, volcanic islands, and large igneous provinces such as the Columbia River Basalts.
