igneous
Basalt
Basalt
Hardness: 5-6 (Mohs); Color: Dark grey to black, weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained) to porphyritic; Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black, weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black, weathering to brown; 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 at or very near the Earth's surface. Most basalt is Cenozoic to Precambrian in age and forms large plateaus or oceanic crust.
Uses & applications
Widely used in construction as aggregate for roads and concrete, railroad ballast, and high-quality building stone. Some varieties are used for stone carving or as thermal insulation (rock wool).
Geological facts
Basalt is the most common rock on Earth's surface and makes up most of the ocean floor. It is also extremely common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight, and fine-grained texture. It often shows columnar jointing or vesicular (pitted) surfaces when fresh. Common in volcanic regions like Hawaii, the Pacific Northwest, and Iceland.
