Quartz Pebble (Chalcedony/Agate)

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.

Identified on: 4/13/2026

Mode: Standard