igneous
Basalt Pebble
Basalt
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained, microcrystalline matrix of plagioclase feldspar, pyroxene, and olivine); Cleavage: None visible.
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to black, sometimes weathering to brown
- Luster
- Dull to sub-metallic
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to black, sometimes weathering to brown; Luster: Dull to sub-metallic; Crystal Structure: Aphanitic (fine-grained, microcrystalline matrix of plagioclase feldspar, pyroxene, and olivine); Cleavage: None visible.
Formation & geological history
Formed from the rapid cooling of low-viscosity basaltic lava at or near the Earth's surface. Pebbles like this specimen have been rounded and smoothed over time by stream, river, or coastal wave action.
Uses & applications
Commonly used as crushed aggregate in road construction, concrete, railroad ballast, and decorative landscaping rock.
Geological facts
Basalt is the most common rock type in the Earth's crust, forming almost all of the oceanic crust as well as vast continental flood basalts.
Field identification & locations
Identified by its dark color, high density, smooth stream-worn shape, and fine-grained texture with occasional quartz or calcite micro-veins. Frequently found along gravel beaches, riverbeds, and volcanic regions.
