igneous
Basalt (River Stone)
Basalt
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull/matte; Crystal structure: aphanitic (fine-grained); Specific Gravity: 2.8–3.0. This specimen shows a rounded, water-worn texture.
- Hardness
- 6-7 Mohs
- Color
- dark grey to black
- Luster
- dull/matte
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull/matte; Crystal structure: aphanitic (fine-grained); Specific Gravity: 2.8–3.0. This specimen shows a rounded, water-worn texture.
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. The rounded shape indicates erosion in a high-energy aquatic environment such as a river or beach.
Uses & applications
Commonly used in construction as aggregate, for road base, concrete, and railroad ballast. Smooth river-worn basalt is often used in landscaping and massage therapy.
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 on the Moon, Mars, and Venus.
Field identification & locations
Identify in the field by its high density, dark color, and fine-grained texture. Found globally in volcanic regions and riverbeds downstream from volcanic sources.
