sedimentary
Yellow Chalcedony (Agate/Chert)
Silicon Dioxide (SiO2) - Cryptocrystalline Quartz
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
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Physical properties
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.
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.
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