igneous
Beach Pebble (Basalt / Volcanic Rock)
Aphanitic Igneous Rock / Basalt
Hardness: 6 on Mohs scale. Color: Dark gray to brownish-gray. Luster: Dull to sub-vitreous. Crystal structure: Microcrystalline or cryptocrystalline (aphanitic). Cleavage: None. Specific gravity: 2.8-3.0.
- Hardness
- 6 on Mohs scale
- Color
- Dark gray to brownish-gray
- Luster
- Dull to sub-vitreous
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Physical properties
Hardness: 6 on Mohs scale. Color: Dark gray to brownish-gray. Luster: Dull to sub-vitreous. Crystal structure: Microcrystalline or cryptocrystalline (aphanitic). Cleavage: None. Specific gravity: 2.8-3.0.
Formation & geological history
Formed from the rapid cooling of mafic lava exposed at or very near the Earth's surface. This particular specimen has been smoothed and rounded by wave action over a long period in a high-energy littoral (beach) environment.
Uses & applications
Used in landscaping, decorative pathways, saunas, and construction aggregate.
Geological facts
Basalt is the most common volcanic rock type in the Earth's crust, forming most of the oceanic crust and major volcanic islands such as Hawaii and Iceland. Similar smooth pebbles are often collected for skipping stones or crafting.
Field identification & locations
Found abundantly on beaches, riverbeds, and glacial outwash plains worldwide. Identified by its fine-grained texture, dark coloration, and smooth, rounded shape caused by water tumbling.
