Mineral

Quartz Pebble (Chalcedony/Agate)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale); Color: Tan, cream, translucent orange; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Tan, cream, translucent orange
Luster: Waxy to vitreous

Identified April 13, 2026More mineral →

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Physical properties

Hardness: 7 (Mohs scale); Color: Tan, cream, translucent orange; Luster: Waxy to vitreous; Crystal structure: Trigonal/Microcrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed through the precipitation of silica from groundwater or hydrothermal fluids in cavities of other rocks. As a rounded pebble, it has been weathered and tumbled by water over many centuries.

Uses & applications

Commonly used in tumble polishing for collectors, as aquarium gravel, or as industrial abrasives. Larger high-quality versions are used in jewelry.

Geological facts

Quartz is one of the most abundant minerals on Earth's crust. Microcrystalline varieties like this one, when tumbled in a river, lose their sharp edges and take on a soft, waxy texture.

Field identification & locations

Identify in the field by its hardness (it will scratch glass) and its smooth, rounded 'water-worn' appearance. Found globally in riverbeds, beaches, and glacial deposits.

Other mineral specimens

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Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Epidote

Epidote | Ca2(Al2,Fe3+)(SiO4)(Si2O7)O(OH)

metamorphic

Nephrite Jade

Nephrite

Mineral/Rock

Banded Gneiss (River Rock/Pebble)

Gneiss (specifically a banded variety often found as a river rock)

Metamorphic Rock

Green Apatite on Albite

Fluorapatite [Ca5(PO4)3F] on Albite [Na(AlSi3O8)]

mineral