igneous
Basalt River Stone
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6.0-7.0 (Mohs scale); Color: Black to dark charcoal grey; Luster: Dull to sub-vitreous; Structure: Fine-grained (aphanitic) or glassy; Specific Gravity: 2.8–3.0.
- Hardness
- 6
- Color
- Black to dark charcoal grey
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6.0-7.0 (Mohs scale); Color: Black to dark charcoal grey; Luster: Dull to sub-vitreous; Structure: Fine-grained (aphanitic) or glassy; Specific Gravity: 2.8–3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava (magma) exposed at or very near the surface of a terrestrial planet or a moon. This specific specimen has been further shaped by fluvial (river) erosion, resulting in its smooth, rounded 'pebble' or 'river rock' texture.
Uses & applications
Used widely in construction (aggregate), high-end landscaping, river rock decor, massage stone therapy, and as raw material for stone tool replication/demonstration.
Geological facts
Basalt is the most common volcanic rock on Earth and makes up most of the ocean floor. It is also found on the Moon, Mars, and Venus. The smooth surface of a river stone takes thousands of years of tumbling against other rocks to achieve.
Field identification & locations
Identify in the field by its significant weight (density), dark color, and fine-grained texture that lacks visible crystals to the naked eye. In riverbeds, it is distinguished by its extreme hardness and resistance to breaking compared to sedimentary pebbles. Found globally in volcanic regions and associated river systems.
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