igneous
Beach Pebble (likely Basalt or Chert)
Volcanic Basalt / Microcrystalline Quartz
Hardness: 6-7 Mohs; Color: Dark brown to black; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained); Shape: Smooth, water-worn/rounded.
- Hardness
- 6-7 Mohs
- Color
- Dark brown to black
- Luster
- Dull to sub-vitreous
Identified More igneous →
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Physical properties
Hardness: 6-7 Mohs; Color: Dark brown to black; Luster: Dull to sub-vitreous; Structure: Aphanitic (fine-grained); Shape: Smooth, water-worn/rounded.
Formation & geological history
Formed through rapid cooling of magnesium-rich and iron-rich lava (if basalt) or silica precipitation (if chert). It has been mechanically weathered and rounded by wave action over decades or centuries.
Uses & applications
Primarily used for decorative landscaping, beach preservation, and occasionally as a tumbling medium for rock collectors.
Geological facts
The smoothness of beach pebbles is a result of 'abrasion,' where rocks collide with each other in the surf, wearing down sharp edges into rounded surfaces.
Field identification & locations
Identify by its heavy weight relative to size, dark uniform color, and extremely smooth surface. Frequently found on volcanic or high-energy coastlines.
