igneous
Basalt
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 6.0-7.0 (Mohs); Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained), often containing plagioclase feldspar and pyroxene; Specific Gravity: 2.8-3.0.
- Hardness
- 6
- Color
- Dark grey to charcoal black
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6.0-7.0 (Mohs); Color: Dark grey to charcoal black; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained), often containing plagioclase feldspar and pyroxene; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a terrestrial planet or moon. Most basalt found on Earth is from the Cenozoic era, though it exists across all geological ages.
Uses & applications
Primarily used in construction for aggregate, road base, railroad ballast, and high-quality asphalt. It is also used in the manufacturing of stone wool insulation and occasionally as decorative landscaping stone.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It is also prevalent on Mars and the Moon, where it forms the dark lunar maria visible from Earth.
Field identification & locations
Identify in the field by its heavy weight (high density), dark color, and fine-grained texture. It often shows columnar jointing or vesicular (pitted) surfaces when fresh, though river-worn pieces like this appear smooth and rounded.
