igneous
Basalt
Basalt (SiO2 percentage between 45% and 52%)
Hardness: 6 on Mohs scale; Color: Dark grey to black, often weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained), often contains micro-crystals of plagioclase feldspar and pyroxene; Cleavage: None (conchoidal fracture); Specific gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, often weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black, often weathering to brown; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained), often contains micro-crystals of plagioclase feldspar and pyroxene; Cleavage: None (conchoidal fracture); 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 specimens range from the Archean Eon to recent volcanic eruptions.
Uses & applications
Used primarily in construction for aggregate, road base, railroad ballast, and floor tiles. It is also used as cast basalt for industrial wear-resistant liners.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. It also covers large areas of the Moon (the Lunar Maria), Mars, and Venus.
Field identification & locations
Identify in the field by its dark weight and fine-grained texture; it may have small holes (vesicles) if gas bubbles were trapped during cooling. Found globally in volcanic regions like the Pacific Northwest of the USA, Iceland, and Hawaii.
