igneous
Grey Basalt Pebble
Basalt (Aphanitic Mafic Volcanic Rock)
Hardness: 5-6 Mohs. Color: Medium to dark grey. Luster: Dull/Matte. Structure: Microcrystalline (aphanitic). Cleavage: None. Specific Gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Medium to dark grey
- Luster
- Dull/Matte
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Physical properties
Hardness: 5-6 Mohs. Color: Medium to dark grey. Luster: Dull/Matte. Structure: Microcrystalline (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 or very near the Earth's surface. This specimen has been water-worn into a smooth, rounded pebble shape through fluvial or marine erosion.
Uses & applications
Used primarily in construction as aggregate, road base, and railroad ballast. Smooth basalt pebbles are popular in 'hot stone' massage therapy and decorative landscaping.
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 heavy weight relative to size, fine-grained texture with no visible crystals, and grey-to-black color. Commonly found on beaches and in riverbeds in volcanic regions.
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