igneous
Basalt
Basalt (mafic volcanic rock)
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to earthy. Structure: fine-grained (aphanitic), often with vesicles (tiny holes). Cleavage: none. Specific gravity: 2.8 - 3.0.
- Hardness
- 5-6 Mohs
- Color
- dark grey to black
- Luster
- dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: dark grey to black. Luster: dull to earthy. Structure: fine-grained (aphanitic), often with vesicles (tiny holes). Cleavage: none. 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. Common in oceanic crust and volcanic arcs.
Uses & applications
Extensively used in construction as aggregate, road base, railroad ballast, and for high-quality floor tiles and statues. Occasionally used in jewelry as 'lava stone'.
Geological facts
Basalt is the most common rock type in Earth's crust and also makes up most of the surface of the Moon (the dark lunar maria) and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and very fine-grained texture. It often weathers to a reddish-brown color on the surface. Find it in volcanic fields or as river-worn cobbles.
