mineral
Chalcedony (Agate / Quartz Geode Fragment)
Silicon Dioxide (SiO2)
Hardness: 6.5-7 on Mohs scale. Color: Translucent milky white to pale yellowish-grey with iron-oxide staining. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.58-2.64.
- Hardness
- 6
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 6.5-7 on Mohs scale. Color: Translucent milky white to pale yellowish-grey with iron-oxide staining. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.58-2.64.
Formation & geological history
Forms at relatively low temperatures through the deposition of silica-rich hydrothermal fluids or groundwater filling cavities, vugs, or gas bubbles in volcanic or sedimentary rocks over thousands to millions of years.
Uses & applications
Used in lapidary arts for carving, tumbled stones, jewelry beads, and decorative mineral collection specimens. Industrially used historically for mortars and pestles due to hardness.
Geological facts
Chalcedony is composed of fine intergrowths of quartz and moganite. The hollow cavities (vugs) visible in this piece are characteristic of small geode formations or vesicular basalt cavities where silica precipitated.
Field identification & locations
Identified by its waxy luster, hardness (scratches glass, cannot be scratched by steel), translucent edges, and microcrystalline structure without distinct large crystal faces. Found worldwide in volcanic terrains, river beds, and desert gravels.
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