Chalcedony

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Milky white to tan; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6-2.64

Formation & Geological History

Formed by the deposition of silica from water solutions in cavities and veins within both volcanic and sedimentary rocks. It often forms at relatively low temperatures near the Earth's surface.

Uses & Applications

Used frequently as a gemstone for jewelry (cabochons, beads), ornamental carvings, and historically for making sharp tools or weapons.

Geological Facts

Chalcedony is an umbrella term that includes agate, jasper, and carnelian. It was used in the ancient world for making cylinder seals and signet rings because hot wax does not stick to it.

Field Identification & Locations

Identify in the field by its waxy luster, conchoidal fracture (curved surfaces like glass), and its ability to scratch glass. Commonly found in desert washes and volcanic regions worldwide.

Identified on: 5/19/2026

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