igneous
Basalt (River Stone)
Extrusive mafic igneous rock
Hardness: 6-7 on Mohs scale; Color: Dark grey to blackish-brown; 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 blackish-brown
- Luster
- Dull to sub-metallic
Identified More igneous →
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Physical properties
Hardness: 6-7 on Mohs scale; Color: Dark grey to blackish-brown; 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 very near the Earth surface. This specimen appears water-worn, suggesting a secondary transport via fluvial (river) environments.
Uses & applications
Crushed stone for road base, concrete aggregate, railroad ballast, and decorative landscaping or river rock gardens.
Geological facts
Basalt is the most common rock type in the Earth's crust and also makes up most of the ocean floor. It is found on the Moon and Mars as well.
Field identification & locations
Identify in the field by its heavy weight (density), dark color, and lack of visible crystals. Commonly found in volcanic regions or in riverbeds downstream from volcanic sources.
