igneous
River Stone (Basalt)
Extrusive Igneous Rock (Mafic)
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal brown; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to charcoal brown
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal brown; Luster: Dull to sub-vitreous; 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 the earth's surface. This specimen has been naturally tumbled and smoothed by water erosion in a river or coastal environment.
Uses & applications
Commonly used for landscaping, decorative garden stones, masonry, drainage systems, and as an abrasive in industrial applications.
Geological facts
Basalt is the most common rock in 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 ubiquitous in volcanic regions and along riverbeds downstream from volcanic mountain ranges.
