igneous
Basalt River Stone
Basalt
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to earthy; Structure: fine-grained (aphanitic); Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- dark grey to black
- Luster
- dull to earthy
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black; Luster: dull to earthy; Structure: fine-grained (aphanitic); Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or very near the Earth's surface. This specific specimen has been rounded and smoothed by water erosion in a river or coastal environment.
Uses & applications
Used extensively in construction as aggregate, for road base, and as decorative landscaping stones. Tumbled versions are popular for 'hot stone' massage therapy due to heat retention.
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 and Mars.
Field identification & locations
Identify by its heavy weight (density), dark uniform color, and fine-grained texture. It often shows small pits (vesicles) or a smooth, water-worn surface when found near water.
