igneous
Basalt River Pebble
Basalt (extrusive volcanic rock)
Hardness: 6-7 Mohs; Color: dark grey to black/greenish-grey; Luster: dull to earthy; Crystal structure: fine-grained (aphanitic); Specific gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- dark grey to black/greenish-grey
- Luster
- dull to earthy
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: dark grey to black/greenish-grey; Luster: dull to earthy; Crystal 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 near the Earth's surface. This specific specimen has been rounded and smoothed by water erosion in a river or coastal environment.
Uses & applications
Basalt is used extensively in construction (crushed stone, asphalt, concrete) and as decorative garden stones. Pebbles are popular in landscaping and aquariums.
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 weight (dense for its size), dark uniform color, and fine-grained texture. Commonly found in riverbeds, glacial tills, and volcanic regions.
