mineral
Chalcedony (Agate Nodule)
Silicon Dioxide (SiO2)
Mohs hardness: 6.5 - 7; Color: translucent light grey to pale lavender blue with white microcrystalline banding; Luster: waxy to vitreous; Crystal structure: trigonal/microcrystalline aggregate; Cleavage: none; Conchoidal fracture.
- Hardness
- 6
- Luster
- waxy to vitreous
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Physical properties
Mohs hardness: 6.5 - 7; Color: translucent light grey to pale lavender blue with white microcrystalline banding; Luster: waxy to vitreous; Crystal structure: trigonal/microcrystalline aggregate; Cleavage: none; Conchoidal fracture.
Formation & geological history
Formed via secondary silica deposition from hydrothermal fluids precipitated within the gas cavities (vesicles) of volcanic rocks like basalt or rhyolite.
Uses & applications
Used extensively in gemstone lapidary, cabochon cutting, jewelry, ornamental carvings, and geological collections.
Geological facts
Chalcedony is a cryptocrystalline variety of quartz, meaning its crystals are too small to be seen without significant magnification. When featuring distinct concentric or fine banding, it is classified as agate.
Field identification & locations
Identified by its waxy luster, lack of distinct cleavage planes, translucent body, smooth conchoidal fracture, and ability to scratch glass easily. Commonly found in basaltic lava fields, desert gravels, and riverbeds worldwide.
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