igneous
Basalt River Pebble
Basalt (extrusive igneous rock)
Hardness: 6-7 (Mohs); Color: Dark grey to charcoal with salt-and-pepper flecks; Luster: Dull/earthy; Crystal structure: Fine-grained/aphanitic; Specific gravity: 2.8-3.0
- Hardness
- 6-7 (Mohs)
- Color
- Dark grey to charcoal with salt-and-pepper flecks
- Luster
- Dull/earthy
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Physical properties
Hardness: 6-7 (Mohs); Color: Dark grey to charcoal with salt-and-pepper flecks; Luster: Dull/earthy; 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 very near the Earth's surface. This specific specimen has been rounded by fluvial (river) or coastal erosion.
Uses & applications
Commonly used in construction as aggregate, for road base, and in decorative 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 found extensively on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, heavy weight for its size, and the presence of tiny crystals. Often found in riverbeds, glacial tills, or near volcanic coastlines.
