igneous
Basalt (River Stone)
Basalt
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often with subtle banding when water-worn; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); Specific gravity: 2.8–3.0
- Hardness
- 6-7 on Mohs scale
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to black, often with subtle banding when water-worn; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Cleavage: None (conchoidal fracture); 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 specific specimen has been smoothed by fluvial (river) or coastal water erosion over many years.
Uses & applications
Commonly used in construction as aggregate, in road base, for hot stone massage therapy due to heat retention, and in decorative landscaping.
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 lack of visible crystals. Commonly found in volcanic regions, riverbeds, and beaches near basaltic cliffs. Collectors look for smooth, symmetrical shapes.
