mineral

Chalcedony (Agate/Chert)

Chalcedony (Silicon Dioxide, SiO2)

Hardness: 6.5-7 on Mohs scale. Color: Translucent white to milky tan. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Color: Translucent white to milky tan
Luster: Waxy to vitreous

Identified June 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed from the deposition of silica-rich fluids in cavities of volcanic or sedimentary rocks. It typically precipitates at low temperatures near the Earth's surface.

Uses & applications

Used primarily in lapidary work, jewelry making, ornamental carvings, and historically for making sharp tools and arrowheads due to its fracture patterns.

Geological facts

Chalcedony was named after the ancient Greek town of Chalcedon. It is the broad group that includes better-known varieties like agate, onyx, carnelian, and jasper.

Field identification & locations

Identify in the field by its waxy appearance, smoothness, and the way it breaks into curved 'shell-like' shapes (conchoidal fracture). It will scratch glass but cannot be scratched by a steel knife.

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