Chalcedony / Agate

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Translucent white, grey, or yellowish with brown inclusions; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Specific Gravity: 2.58-2.64

Formation & Geological History

Formed as a chemical precipitate from silica-rich hydrothermal fluids or groundwater, often filling cavities in volcanic or sedimentary rocks over thousands of years.

Uses & Applications

Used primarily in lapidary work for jewelry, cabochons, and decorative ornamental items. Historically used for making stone tools due to its conchoidal fracture.

Geological Facts

The name 'Chalcedony' comes from the ancient Greek town of Chalkedon. It is a microcrystalline form of quartz where the crystals are too small to be seen without high magnification.

Field Identification & Locations

Identify in the field by its translucency, waxy luster, and lack of visible crystal faces. Can be found globally in riverbeds, desert pavements, and volcanic outcrops.

Identified on: 5/1/2026

Mode: Standard