igneous
Basalt Pebble
Basalt
Hardness: 6 on Mohs scale; Color: dark gray to black; Luster: dull to sub-metallic on smooth river-worn surfaces; Texture: fine-grained (aphanitic), micro-porous or vesicular; Specific Gravity: ~2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- dark gray to black
- Luster
- dull to sub-metallic on smooth river-worn surfaces
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Physical properties
Hardness: 6 on Mohs scale; Color: dark gray to black; Luster: dull to sub-metallic on smooth river-worn surfaces; Texture: fine-grained (aphanitic), micro-porous or vesicular; Specific Gravity: ~2.8-3.0.
Formation & geological history
Formed from the rapid cooling of low-viscosity mafic lava at or near Earth's surface, typically at mid-ocean ridges, oceanic islands, or volcanic hotspots. These rounded shapes result from mechanical weathering and transport in rivers or ocean surf.
Uses & applications
Used widely in construction as crushed aggregate, in railway ballast, for asphalt paving, and as decorative river rocks in landscaping and aquariums.
Geological facts
Basalt is the most common rock type in Earth's crust, making up almost the entirety of the ocean floors. It is also extremely common on the Moon and Mars.
Field identification & locations
Identify in the field by its dark color, high density, smooth stream-rounded or beach-worn surface, fine-grained texture, and lack of visible quartz crystals. Extremely abundant on beaches, riverbeds, and volcanic regions worldwide.
