Chalcedony in Host Rock

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Milky white to bluish-grey; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (Trigonal/Monoclinic); Cleavage: None; Fracture: Conchoidal.

Formation & Geological History

Formed through the deposition of silica-rich fluids in cavities or fractures of host rocks (often volcanic or sedimentary). Deposition occurs at relatively low temperatures over millions of years.

Uses & Applications

Commonly used for lapidary work, cabochons for jewelry, ornamental carvings, and historical use for tool making (due to sharpenable edges).

Geological Facts

Chalcedony was highly valued in antiquity; the name is believed to derive from the ancient Greek town of Chalkedon. It is the broad term that includes agate, jasper, and carnelian.

Field Identification & Locations

Identify in the field by its waxy appearance, light translucency on edges, and inability to be scratched by a steel knife. It is frequently found in desert regions, riverbeds, and volcanic outcrops.

Identified on: 4/22/2026

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