igneous
Basalt pebble
Basalt (Mafic Extrusive Igneous Rock)
Hardness: 5-6 Mohs. Color: dark gray to black. Luster: dull to earthy. Crystal structure: fine-grained (aphanitic). Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- dark gray to black
- Luster
- dull to earthy
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Physical properties
Hardness: 5-6 Mohs. Color: dark gray to black. Luster: dull to earthy. Crystal structure: fine-grained (aphanitic). 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 surface of a terrestrial planet or the moon.
Uses & applications
Used in construction aggregate, road base, concrete, and as high-quality railroad ballast.
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 for its size, and lack of visible crystals. It is commonly found in volcanic regions or as water-worn pebbles in rivers near volcanic origins.
