Chalcedony (Agate)

Physical Properties

Hardness: 6.5–7 (Mohs scale); Color: Tans, browns, and whites; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.58–2.64

Formation & Geological History

Formed through the deposition of silica-rich groundwater in cavities of igneous rocks or sedimentary layers. It typically forms at low temperatures over millions of years.

Uses & Applications

Used widely in semi-precious jewelry, lapidary art (cabochons), historical seal carvings, and industrial uses like mortar and pestles due to its hardness.

Geological Facts

Agate is a variety of chalcedony characterized by its translucency and often its banding; even small, unbanded river-worn pebbles like this specimen are part of the chalcedony family.

Field Identification & Locations

Identify in the field by its translucency (light passes through it, as seen in the photo), waxy texture when wet, and conchoidal (shell-like) fracture patterns. Frequently found in gravel pits and riverbeds.

Identified on: 4/13/2026

Mode: Standard