Chalcedony (Pink/Gray variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale. Color: Translucent pinkish-gray. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline microstructures (trigonal). Cleavage: None (conchoidal fracture). Specific gravity: 2.6-2.64.

Formation & Geological History

Formed from the deposition of silica from water at relatively low temperatures, often in volcanic cavities (vesicles) or sedimentary environments like limestone or deep-sea oozes. It can form at any geological age.

Uses & Applications

Used primarily in lapidary work for making cabochons, beads, and carvings. High-quality specimens are used in jewelry. In industry, it was historically used for mortar and pestle sets due to its hardness and durability.

Geological Facts

Chalcedony was highly prized in ancient times; the Romans used it for engraved seals and cameos because it does not stick to hot wax. It is the broad term that also encompasses varieties like agate, onyx, and jasper.

Field Identification & Locations

Identify by its waxy luster, smooth conchoidal (shell-like) fracture, and the fact that it will scratch glass but cannot be scratched by a steel knife. Commonly found in Brazil, India, and the western United States.

Identified on: 4/19/2026

Mode: Standard