igneous
Basalt (Concrete Aggregate)
Basalt (Mafic volcanic rock)
Hardness: 6-7 (Mohs scale); Color: Dark grey, charcoal to black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 6-7 (Mohs scale)
- Color
- Dark grey, charcoal to black
- Luster
- Dull to earthy
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Physical properties
Hardness: 6-7 (Mohs scale); Color: Dark grey, charcoal to black; Luster: Dull to earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. It is the most common rock in Earth's crust, making up most of the ocean floor.
Uses & applications
Primary use as construction aggregate for roads, concrete, and railroad ballast. Also used in high-temperature insulation (stone wool) and as a building stone.
Geological facts
Basalt is found extensively on the Moon and Mars. Most of the Moon's dark plains, the lunar maria, are basaltic lava flows.
Field identification & locations
Identify in the field by its dark color, heavy weight compared to other similar-sized rocks, and lack of visible crystals to the naked eye. In this image, it is seen as crushed rock embedded in a concrete matrix.
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