igneous
Basalt Gravel
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to earthy; Texture: Fine-grained (aphanitic); Specific Gravity: 2.8-3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to earthy
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black; Luster: Dull to earthy; Texture: Fine-grained (aphanitic); Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava exposed at or very near the surface of a terrestrial planet or a moon. It is the most common volcanic rock on Earth.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality concrete. Also used for decorative landscaping and as an additive for aquarium filters.
Geological facts
Basalt is equivalent in composition to gabbro, but differs in that basalt is extrusive and has a much finer grain size. It makes up most of the Earth's oceanic crust.
Field identification & locations
Identified by its dark color, heavy weight for its size, and lack of visible crystals without magnification. Often found in volcanic regions or as imported gravel in urban landscaping.
