igneous
Basalt
Basalt (Mafic volcanic rock)
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Texture: Vesicular or massive.
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull/Earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull/Earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0; Texture: Vesicular or massive.
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 specimens date from the Cenozoic era, though they can be billions of years old.
Uses & applications
Used extensively in construction as crushed stone for road base, railroad ballast, and concrete aggregate. Sometimes used in polished form for floor tiles or monument carvings.
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 found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and fine-grained texture that lacks visible crystals. It is commonly found in volcanic regions, such as the Pacific Northwest, Hawaii, and Iceland.
