igneous
Vesicular Basalt (River Stone)
Basalt (Aphanitic-Vesicular Mafic Rock)
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal, with reddish-brown oxidation in pores; Luster: Dull to earthy; Texture: Fine-grained (aphanitic) with small pits (vesicles); Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to charcoal, with reddish-brown oxidation in pores
- Luster
- Dull to earthy
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to charcoal, with reddish-brown oxidation in pores; Luster: Dull to earthy; Texture: 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 the Earth's surface. The pits called vesicles were formed by gas bubbles trapped in the cooling lava. This specific specimen has been rounded by fluvial erosion in a river or coastal environment.
Uses & applications
Used primarily as construction aggregate, road base, and railroad ballast. Smooth river-worn basalt is popular in landscaping, aquarium decor, and hot stone massage therapy.
Geological facts
Basalt is the most common rock type on the Earth's crust and makes up most of the ocean floors. It is also found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its high density (feels heavy for its size), dark color, and characteristic tiny holes or pits. Commonly found in volcanic regions or in riverbeds downstream from volcanic mountain ranges.
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Dark Igneous Rock (Likely Basalt or Diabase)
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