mineral

Grey Chalcedony

Silicon Dioxide (SiO2)

Hardness: 6.5-7.0 (Mohs scale); Color: Translucent grey to bluish-grey; Luster: Waxy to vitreous; Crystal structure: Trigonal (cryptocrystalline); Cleavage: None; Specific gravity: 2.58-2.64

Hardness: 6
Color: Translucent grey to bluish-grey
Luster: Waxy to vitreous

Identified March 4, 2026More mineral →

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Physical properties

Hardness: 6.5-7.0 (Mohs scale); Color: Translucent grey to bluish-grey; Luster: Waxy to vitreous; Crystal structure: Trigonal (cryptocrystalline); Cleavage: None; Specific gravity: 2.58-2.64

Formation & geological history

Formed through the deposition of silica-rich fluids in volcanic cavities (geodes) or sedimentary environments at relatively low temperatures. It often occurs as botryoidal masses or rounded nodules.

Uses & applications

Used primarily in jewelry as cabochons, decorative carvings, and in industrial applications such as mortar and pestles due to its high hardness and density.

Geological facts

Chalcedony is a cryptocrystalline variety of quartz, meaning its crystals are so small they can only be seen under extreme magnification. It has been used for making tools and seals since the Bronze Age.

Field identification & locations

Identify by its waxy luster, translucency, and inability to be scratched by a steel knife. Common in volcanic regions with agate deposits, often found in stream beds or weathered out of basalt.