igneous
Basalt
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs); Color: Dark grey to black, weathering to brown/green; Luster: Dull/earthy; Structure: Fine-grained (aphanitic) or vesicular; Specific gravity: 2.8 - 3.0
- Hardness
- 6 (Mohs)
- Color
- Dark grey to black, weathering to brown/green
- Luster
- Dull/earthy
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Physical properties
Hardness: 6 (Mohs); Color: Dark grey to black, weathering to brown/green; Luster: Dull/earthy; Structure: Fine-grained (aphanitic) or vesicular; 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 a moon. Most are Cenozoic in age but range throughout Earth's history.
Uses & applications
Commonly used as crushed stone for construction projects, road base, concrete aggregate, and railroad ballast. Also used in high-temp insulation and stone carvings.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floor. Large portions of the Moon and Mars are also covered in basaltic plains.
Field identification & locations
Identify by its heavy weight, dark color, and lack of visible crystals. It often features a weathered 'rind' (crust) that is lighter than the dark interior. Found globally in volcanic regions like Hawaii or the Pacific Northwest.
