mineral

Chalcedony

Silicon Dioxide (SiO₂)

Hardness: 6.5–7 on Mohs scale; Color: Milky white, light grey, or bluish-white; Luster: Waxy to vitreous; Crystal Structure: Trigonal (cryptocrystalline); Cleavage: None; Relief: Translucent to opaque; Specific gravity: 2.58–2.64.

Hardness: 6
Color: Milky white, light grey, or bluish-white
Luster: Waxy to vitreous

Identified March 25, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica-rich fluids in volcanic cavities, lava pockets, or sedimentary environments at relatively low temperatures. It often fills veins or amygdules in igneous rocks.

Uses & applications

Commonly used as a gemstone in jewelry (cabochons), as ornamental carvings, and historically for tools like arrowheads and seals. It is also used as an industrial abrasive and in precision bearings.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are so small they are only visible under a microscope. It includes famous varieties such as Agate, Onyx, and Carnelian.

Field identification & locations

Identify in the field by its waxy luster, lack of visible crystals, and conchoidal (shell-like) fracture. Commonly found in Brazil, India, Madagascar, and the western United States. Collectors should look for unique translucency and uniform color.