igneous
River Stone (Basalt or fine-grained Schist)
Mafic Igneous Rock / Volcanic Basalt
Hardness: 5-6 (Mohs); Color: Dark grey, charcoal, or bluish-black with subtle inclusions; Luster: Dull to earthy (unpolished); Crystal Structure: Aphanitic (fine-grained); Specific Gravity: 2.8 - 3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey, charcoal, or bluish-black with subtle inclusions
- Luster
- Dull to earthy (unpolished)
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey, charcoal, or bluish-black with subtle inclusions; Luster: Dull to earthy (unpolished); 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 the Earth's surface. This specific specimen has been smoothed and rounded by long-term hydraulic action in a river or coastal environment.
Uses & applications
Commonly used in landscaping, as aquarium gravel, in construction as crushed stone aggregate, and in 'hot stone' massage therapy due to high heat retention.
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 smooth, water-worn texture. Commonly found in riverbeds, glacial till, and mountainous coastal regions.
