igneous
Basalt (River Stone)
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull/Matte; Structure: Fine-grained (Aphanitic); Cleavage: None/Irregular; Specific Gravity: 2.8–3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to black; Luster: Dull/Matte; Structure: Fine-grained (Aphanitic); Cleavage: None/Irregular; 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 surface of a terrestrial planet. This specific specimen has been rounded by fluvial (river) erosion, indicating it was likely transported by water over long periods.
Uses & applications
Used in construction as aggregate, for making road bases, as river rock in landscaping, and occasionally in stone massage therapy or as a medium for stone painting.
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up the majority of the ocean floor. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and absence of visible large crystals. It is commonly found in volcanic regions or riverbeds downstream from volcanic sources. Collectors value smooth, ergonomic shapes.
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