igneous
Basalt (River Stone)
Basalt (Mafic volcanic rock)
Hardness: 5-6 Mohs. Color: Dark grey to black. Luster: Dull to sub-metallic when wet. Crystal structure: Aphanitic (fine-grained). Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Dark grey to black
- Luster
- Dull to sub-metallic when wet
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Physical properties
Hardness: 5-6 Mohs. Color: Dark grey to black. Luster: Dull to sub-metallic when wet. 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 very near the surface of a terrestrial planet or a moon. This specimen appears water-worn, likely from a fluvial environment.
Uses & applications
Commonly used as aggregate in construction (roads, concrete), as decorative garden stones, and for stone masonry. Small rounded pieces are often used in hot stone massage.
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
Field identification involves checking for a dark, dense, fine-grained appearance. It is often found in volcanic regions or as rounded cobbles in riverbeds and on beaches.
