sedimentary
Beach Pebble / Agate-bearing Chert Pebble
Microcrystalline Quartz (SiO2) with Inclusion Minerals
Hardness: 6.5-7 on Mohs scale; Color: Mottled brown, tan, translucent white, and dark grey/black patches; Luster: Vitreous to waxy when wet/smooth; Cleavage: None (conchoidal fracture); Specific Gravity: ~2.6-2.75.
- Hardness
- 6
- Luster
- Vitreous to waxy when wet/smooth
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: Mottled brown, tan, translucent white, and dark grey/black patches; Luster: Vitreous to waxy when wet/smooth; Cleavage: None (conchoidal fracture); Specific Gravity: ~2.6-2.75.
Formation & geological history
Formed through the precipitation of silica in sedimentary environments or basaltic cavities, followed by erosion, transport, and natural water-smoothing in rivers or ocean shorelines.
Uses & applications
Primarily collected as a beachcombing keepsake, used in lapidary work for rock tumbling, decorative gravel, and landscape design.
Geological facts
Water-rounded pebbles often travel tens or hundreds of miles down rivers to beaches, undergoing continuous natural polishing along the way.
Field identification & locations
Look for rounded, smooth shapes with translucent patches of chalcedony/quartz and dark inclusions. Commonly found on ocean beaches, lake shores, and river beds worldwide. Tumbles well in a rock tumbler.
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