igneous
Basalt (tumbled/water-worn)
Extrusive mafic igneous rock
Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull to sub-vitreous; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8–3.0.
- Hardness
- 6
- Color
- dark grey to black
- Luster
- dull to sub-vitreous
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Physical properties
Hardness: 6.0 on Mohs scale; Color: dark grey to black; Luster: dull to sub-vitreous; 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 exposed at or very near the surface of a terrestrial planet or a moon. This specimen appears water-worn or tumbled, suggesting a fluvial or coastal environment.
Uses & applications
Used primarily in construction for aggregate, road base, and railroad ballast. Smooth specimens are popular for hot stone massage therapy and decorative landscaping.
Geological facts
Basalt is the most common rock type in the Earth's crust and covers most of the ocean floor. It is also found on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight (density), and lack of visible crystals to the naked eye. Commonly found in volcanic regions, along shorelines, and in riverbeds.
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