igneous
Basalt River Pebble (with Quartz Vein)
Basalt (Mafic Volcanic Rock)
Hardness: 5-6 Mohs. Color: Black to dark grey. Luster: Dull to waxy when wet. Crystal structure: Aphanitic (fine-grained). Specific gravity: 2.8-3.0.
- Hardness
- 5-6 Mohs
- Color
- Black to dark grey
- Luster
- Dull to waxy when wet
Identified More igneous →
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Physical properties
Hardness: 5-6 Mohs. Color: Black to dark grey. Luster: Dull to waxy when wet. Crystal structure: Aphanitic (fine-grained). 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 pebble has been rounded by fluvial (river) or coastal erosion. The thin band is a hydrothermal quartz or calcite vein formed later.
Uses & applications
Commonly used as river rock for landscaping, aquarium decor, and in construction as aggregate. Some are used for hot stone massage 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
Identify in the field by its dark color, heavy weight (density), and fine-grained texture. Commonly found in riverbeds, glacial tills, and volcanic regions.
