Chalcedony (Quartz variety)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Milky white to bluish-grey; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline (Trigonal/Monoclinic); Cleavage: None; Specific Gravity: 2.58–2.64.

Formation & Geological History

Formed from the deposition of silica-rich water in volcanic cavities (vesicles), sedimentary rocks, and hydrothermal veins. It typically forms at relatively low temperatures.

Uses & Applications

Used in jewelry (cabochons and beads), ornamental carvings, hardstone carving, and historically for tools like arrowheads and seals.

Geological Facts

Chalcedony has been used since the Bronze Age; the Romans used it for signet rings because wax wouldn't stick to the stone. It is the broad term for several varieties including agate and carnelian.

Field Identification & Locations

Identify by its waxy luster, conchoidal fracture (curved glass-like breaks), and lack of visible crystals. Commonly found in Brazil, India, Madagascar, and the USA (Pacific Northwest).

Identified on: 4/22/2026

Mode: Standard