igneous
Basalt (Polished River Stone)
Aphanitic Mafic Igneous Rock
Hardness: 5-6 Mohs. Color: Charcoal grey to black. Luster: Dull (naturally) to sub-vitreous (when polished). Crystal structure: Fine-grained/aphanitic. Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Charcoal grey to black
- Luster
- Dull (naturally) to sub-vitreous (when polished)
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Physical properties
Hardness: 5-6 Mohs. Color: Charcoal grey to black. Luster: Dull (naturally) to sub-vitreous (when polished). Crystal structure: Fine-grained/aphanitic. 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 Earth's surface. This specific specimen has been smoothed by water erosion in a river or tumbled mechanically.
Uses & applications
Used in construction, road base, river rock landscaping, decorative gravel, and occasionally for 'hot stone' massage therapy due to 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 extensively on the Moon and Mars.
Field identification & locations
Identify by its weight (dense), dark color, and lack of visible large crystals. Commonly found in volcanic regions, beaches with volcanic sand, or riverbeds descending from volcanic mountains.
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