igneous
Basalt (River Stone)
Extrusive mafic igneous rock
Hardness: 6 (Mohs scale); Color: charcoal grey to black; Luster: matte/dull; Crystal structure: fine-grained (aphanitic) or glassy; Specific gravity: 2.8-3.0; Texture: smooth, river-worn surface.
- Hardness
- 6 (Mohs scale)
- Color
- charcoal grey to black
- Luster
- matte/dull
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Physical properties
Hardness: 6 (Mohs scale); Color: charcoal grey to black; Luster: matte/dull; Crystal structure: fine-grained (aphanitic) or glassy; Specific gravity: 2.8-3.0; Texture: smooth, river-worn surface.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the Earth's surface. This specimen has been rounded and smoothed by water erosion in a river or coastal environment.
Uses & applications
Used in landscaping, road construction as aggregate, decorative masonry, and aquarium decor. Historically used as a material for tools and building structures.
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 heavy weight (for its size), dark grey to black color, and fine-grained texture. It often lacks visible crystals to the naked eye. Commonly found in former volcanic regions and riverbeds.
