igneous
Basalt (River Pebble)
Extrusive mafic igneous rock
Hardness: 6.0; Color: Dark grey to charcoal; Luster: Dull/Matte; Crystal structure: Aphanitic (fine-grained); Cleavage: None; Specific Gravity: 2.8-3.0.
- Hardness
- 6
- Color
- Dark grey to charcoal
- Luster
- Dull/Matte
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Physical properties
Hardness: 6.0; Color: Dark grey to charcoal; Luster: Dull/Matte; 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 the Earth's surface. This specific specimen has been rounded and smoothed by water erosion in a river or coastal environment.
Uses & applications
Used in construction as aggregate, for road base, in concrete, and as heat-retaining stones in spas or saunas.
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 heavy weight (density), dark color, and fine-grained texture. It often feels slightly gritty despite being polished by water. Commonly found in volcanic regions and riverbeds.
