igneous
Basalt Pebble
Aphanitic Mafic Volcanic Rock (Basalt)
Hardness: 5-6 (Mohs); Color: Dark grey to black, greenish when weathered; Luster: Dull/Matte; Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8-3.0; Cleavage: None
- Hardness
- 5-6 (Mohs)
- Color
- Dark grey to black, greenish when weathered
- Luster
- Dull/Matte
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Physical properties
Hardness: 5-6 (Mohs); Color: Dark grey to black, greenish when weathered; Luster: Dull/Matte; Crystal structure: Fine-grained/Aphanitic; Specific gravity: 2.8-3.0; Cleavage: None
Formation & geological history
Formed from the rapid cooling of magnesium-rich and iron-rich lava at or near the surface of a planet or moon. These pebbles are typically shaped by water erosion in rivers or coastal environments.
Uses & applications
Commonly used as crushed stone for construction, aggregate in concrete and asphalt, and in river rock landscaping or aquarium decor.
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 extremely common on the Moon and Mars.
Field identification & locations
Identify by its dark color, heavy weight for its size, and lack of visible large crystals. Most common in volcanic regions, riverbeds, and beaches near oceanic crust.
