Chalcedony

Physical Properties

Hardness: 6.5-7 Mohs; Color: Pale translucent grey to yellowish; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.6

Formation & Geological History

Formed via the deposition of silica from water in cavities of igneous and sedimentary rocks at low temperatures. Common in volcanic pockets or as petrified bone/wood replaced by silica.

Uses & Applications

Used extensively in jewelry as gemstones, in the manufacturing of clock movements, professional decorative carvings, and as a collectible mineral specimen.

Geological Facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without extreme magnification. It has been used for making tools and seals since the Bronze Age.

Field Identification & Locations

Identify by its waxy luster, conchoidal fracture, and translucency. It is common in riverbeds, desert regions, and volcanic areas like Oregon or Brazil. Collectors look for unique banding or inclusions.

Identified on: 5/10/2026

Mode: Standard