sedimentary

Yellow Chalcedony (Agate/Chert)

Silicon Dioxide (SiO2) - Cryptocrystalline Quartz

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale. Color: Waxy yellow to honey-brown. Luster: Vitreous to waxy. Crystal structure: Hexagonal (microscopic). Cleavage: None (conchoidal fracture). Specific gravity: 2.6 - 2.64.

Hardness: 6
Color: Waxy yellow to honey-brown
Luster: Vitreous to waxy

Identified April 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich groundwater in the cavities of volcanic or sedimentary rocks. It precipitate at relatively low temperatures.

Uses & applications

Used primarily for lapidary work, jewelry (cabochons), as collector specimens, and historically for stone tools due to its sharp conchoidal fracture.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without high magnification. Yellow varieties are often colored by iron oxide (limonite) inclusions.

Field identification & locations

Identify in the field by its waxy luster, smoothness, and the way it breaks into curved, glass-like shards (conchoidal fracture). It will not be scratched by a steel knife.