igneous
Basalt
Mafic Igneous Rock (composed primarily of pyroxene and plagioclase)
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull to sub-metallic; 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. Most basalt dates from the Cenozoic era, though it has formed throughout Earth's history.
Uses & applications
Used primarily in construction for aggregate, road base, railroad ballast, and high-quality concrete. Can be polished for use in floor tiles or wall cladding.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, fine grain size, and heavy weight relative to its size. Commonly found in volcanic regions, oceanic islands, and mid-ocean ridges.
