igneous
Basalt Pebble
Basalt (Mafic volcanic rock)
Hardness: 6-7 Mohs; Color: Dark gray to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.
- Hardness
- 6-7 Mohs
- Color
- Dark gray to black
- Luster
- Dull or earthy
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Physical properties
Hardness: 6-7 Mohs; Color: Dark gray to black; Luster: Dull or earthy; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the Earth's surface. This specimen appears water-worn, likely from a riverbed or coastal environment.
Uses & applications
Commonly used in construction as crushed stone, road base, or concrete aggregate. Polished versions are used in massage therapy (hot stones).
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight compared to other pebbles, and fine-grained texture. It is ubiquitous in volcanic regions and along shorelines.
