igneous
Basalt River Pebble
Basalt (Mafic volcanic rock)
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to earthy; Texture: Fine-grained (aphanitic); Specific Gravity: 2.8-3.0
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull to earthy
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull to earthy; Texture: 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 near the Earth's surface. This specific specimen has been rounded by fluvial (river) or coastal erosion.
Uses & applications
Commonly used in construction as aggregate, for road base, in garden landscaping, and occasionally as hot massage stones.
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
Identified by its dark color, heavy weight for its size, and lack of visible large crystals. Most common in volcanic regions and riverbeds transporting volcanic debris.
