Chalcedony (Agate Pebble)

Physical Properties

Hardness: 6.5–7 on the Mohs scale; Color: Translucent yellow to honey-tan; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.6–2.64

Formation & Geological History

Formed from the deposition of silica-rich water in cavities or veins within volcanic or sedimentary rocks. This specimen is water-worn, likely from a river or beach environment.

Uses & Applications

Used for lapidary work (cabochons), jewelry (tumbled stones), and as a mineral collector's specimen.

Geological Facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a microscope. It is often the base material for agates, carnelians, and jaspers.

Field Identification & Locations

Identify in the field by its translucency (light passes through it), waxy surface texture, and inability to be scratched by a steel knife. Commonly found in riverbeds and gravel pits.

Identified on: 4/25/2026

Mode: Standard