igneous
Basalt River Pebble
Extrusive mafic igneous rock
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull/Matte (tumbled); Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black
- Luster
- Dull/Matte (tumbled)
Identified More igneous →
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black; Luster: Dull/Matte (tumbled); Structure: Aphanitic (fine-grained); Specific Gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the surface. This specific specimen has been rounded and smoothed by fluvial (river) erosion over many years.
Uses & applications
Common pebbles are used in landscaping, aquarium decor, and as 'worry stones'. Crushed basalt is used in construction and road base.
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 extensively on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and lack of visible crystals. It is ubiquitous in volcanic regions and riverbeds.
