igneous
Basalt pebble
Basalt (Mafic volcanic rock)
Hardness: 5-6 Mohs; Color: Dark gray to charcoal; Luster: Dull to sub-metallic when wet; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific gravity: 2.8-3.0
- Hardness
- 5-6 Mohs
- Color
- Dark gray to charcoal
- Luster
- Dull to sub-metallic when wet
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs; Color: Dark gray to charcoal; Luster: Dull to sub-metallic when wet; Crystal structure: Aphanitic (fine-grained); 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. This specimen shows signs of mechanical weathering and rounding by water or transport.
Uses & applications
Commonly used as crushed stone for road base, railroad ballast, and concrete aggregate. High-quality basalt is used in the manufacture of stone wool insulation.
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
Identified in the field by its dark color, heavy weight (relative to size), and fine-grained texture that lacks visible crystals to the naked eye. Found worldwide in volcanic regions.
