igneous
Basalt (River Stone)
Vesicular Basalt
Hardness: 5-6 Mohs. Color: dark gray to black. Luster: dull/earthy. Structure: fine-grained (aphanitic) with small pits (vesicles). Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- dark gray to black
- Luster
- dull/earthy
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Physical properties
Hardness: 5-6 Mohs. Color: dark gray to black. Luster: dull/earthy. Structure: fine-grained (aphanitic) with small pits (vesicles). 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 Earth's surface. This specific specimen has been rounded by fluvial (river) erosion over many years.
Uses & applications
Commonly used in construction as aggregate, for road base, and in decorative landscaping or river-rock gardens.
Geological facts
Basalt is the most common rock type in the Earth's crust and also covers large areas of the Moon's surface (the lunar maria).
Field identification & locations
Identify by its dark color, heavy weight for its size, and the presence of small holes (vesicles) where gas was trapped in the lava. Found globally in volcanic regions and riverbeds.
