sedimentary (mineraloid/microcrystalline quartz)
Yellow Chalcedony (common opal or chert variant)
Silicon Dioxide (SiO2)
Hardness: 6.5–7 on the Mohs scale; Color: mustard yellow to pale yellow with white inclusions; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6–2.7
- Hardness
- 6
- Color
- mustard yellow to pale yellow with white inclusions
- Luster
- waxy to dull
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Physical properties
Hardness: 6.5–7 on the Mohs scale; Color: mustard yellow to pale yellow with white inclusions; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.6–2.7
Formation & geological history
Formed at low temperatures through the deposition of silica from groundwater in cavities of igneous rocks or sedimentary layers. Often associated with volcanic ash beds or hydrothermal activity.
Uses & applications
Used primarily in lapidary work for cabochons, beads, and decorative carvings. It is also a popular specimen for rock tumbling and metaphysical crystal collecting.
Geological facts
Yellow chalcedony is often found alongside dendritic or moss agate. The yellow coloration is typically caused by tiny inclusions of iron oxide minerals like goethite or limonite within the silica structure.
Field identification & locations
Identify in the field by its waxy luster, smooth 'shell-like' conchoidal fracture, and inability to be scratched by a steel knife. Commonly found in Oregon (USA), Brazil, and India. Collectors should look for translucency near the edges.
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