igneous
Basalt Pebble (River Rock / Beach Stone)
Basalt (fine-grained mafic igneous rock)
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Matte, dull to sub-vitreous when wet; Texture: Very fine-grained (aphanitic), extremely smooth due to water erosion; Specific Gravity: 2.8 - 3.0
- Hardness
- 6 on Mohs scale
- Color
- Dark grey to charcoal black
- Luster
- Matte, dull to sub-vitreous when wet
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Physical properties
Hardness: 6 on Mohs scale; Color: Dark grey to charcoal black; Luster: Matte, dull to sub-vitreous when wet; Texture: Very fine-grained (aphanitic), extremely smooth due to water erosion; 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. Rounded over long periods by the abrasive action of flowing water in rivers, streams, or ocean waves.
Uses & applications
Commonly used as worry stones, landscaping pebbles, aquarium gravel, decorative stones, or massage stones due to high heat retention.
Geological facts
Basalt is the most common rock type in the Earth's crust, making up most of the ocean floor. Water-worn pebbles often feature natural indentations that make them popular as stress-relieving 'worry stones'.
Field identification & locations
Identified by its uniform dark grey color, fine-grained texture, matte surface, and rounded, water-smoothed shape. Extremely common along riverbeds, coastlines, and glacial till worldwide.
