igneous
Basalt River Pebble
Basalt (Aphanitic Mafic Igneous Rock)
Hardness: 6-7 Mohs; Color: Dark grey to dull black; Luster: Dull/Matte; Crystal structure: Fine-grained/Aphanitic; Cleavage: None; Specific Gravity: 2.8-3.0
- Hardness
- 6-7 Mohs
- Color
- Dark grey to dull black
- Luster
- Dull/Matte
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Physical properties
Hardness: 6-7 Mohs; Color: Dark grey to dull black; Luster: Dull/Matte; Crystal structure: Fine-grained/Aphanitic; Cleavage: None; Specific Gravity: 2.8-3.0
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at the earth's surface. This specific specimen has been rounded by fluvial (river) or lacustrine (lake) erosion over thousands of years.
Uses & applications
Basalt is used extensively in construction for aggregate, road base, and railroad ballast. Smooth pebbles like this are often used in landscaping, aquariums, and decorative stone 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 and Mars.
Field identification & locations
Identified in the field by its dark color, heavy weight (density), and fine-grained texture. Commonly found in volcanic regions or transported to riverbeds and beaches. Collectors should look for its characteristic dark, uniform matrix.
