igneous
Basalt River Pebble
Basalt
Hardness: 6-7 on Mohs scale; Color: Dark grey to greenish-black; Luster: Dull to sub-metallic; Crystal structure: Aphanitic (fine-grained); Specific gravity: 2.8-3.0
- Hardness
- 6-7 on Mohs scale
- Color
- Dark grey to greenish-black
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to greenish-black; Luster: Dull to sub-metallic; 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 near the Earth's surface. This specific specimen has been rounded by fluvial (river) erosion over many years.
Uses & applications
Commonly used in construction as aggregate for concrete and asphalt, as railroad ballast, and in landscaping. Polished stones are sometimes used in spa treatments (hot stone massage).
Geological facts
Basalt is the most common rock type in the Earth's crust and makes up most of the ocean floors. It is also found extensively on the Moon and Mars.
Field identification & locations
Identified in the field by its heavy weight, dark color, and fine-grained texture. Often found in riverbeds near volcanic regions or coastal areas.
