igneous
Basalt Water-Worn Pebble
Aphanitic Mafic Igneous Rock
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte (sub-metallic when wet); Crystal Structure: Fine-grained/Aphanitic; Specific Gravity: 2.8-3.0
- Hardness
- 6 (Mohs scale)
- Color
- Dark grey to black
- Luster
- Dull/Matte (sub-metallic when wet)
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Physical properties
Hardness: 6 (Mohs scale); Color: Dark grey to black; Luster: Dull/Matte (sub-metallic when wet); 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 by fluvial or marine erosion over thousands of years.
Uses & applications
Commonly used in construction aggregate, road base, shoreline protection (riprap), and as decorative landscaping stones or river rocks.
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 in the field by its dark color, heavy weight (density), and lack of visible large crystals. Often found in riverbeds, beaches, or volcanic fields.
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