igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, weathering to brown or green; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0.
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to black, weathering to brown or green
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, weathering to brown or green; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; 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 moon. Most basalt on Earth was formed during the Cenozoic era, though it spans all geological ages.
Uses & applications
Extensively used in construction for aggregate, road base, railroad ballast, and high-quality asphalt. It is also used as a dimension stone for floor tiles and monuments.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. It is also present on the Moon and Mars, where it forms the 'maria' (dark plains).
Field identification & locations
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. It often shows columnar jointing or vesicular (pitted) surfaces in natural outcrops.
