mineral

Chalcedony

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Translucent grayish-white, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline (Trigonal), Cleavage: None, Specific gravity: 2.58-2.64

Hardness: 6

Identified June 28, 2026More mineral →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Translucent grayish-white, Luster: Waxy to vitreous, Crystal structure: Cryptocrystalline (Trigonal), Cleavage: None, Specific gravity: 2.58-2.64

Formation & geological history

Formed from the deposition of silica from water in fissures or cavities of various rocks, particularly volcanic rocks. It forms at relatively low temperatures.

Uses & applications

Used primarily in jewelry (cabochons), as an ornamental stone, and in abrasive polishing compounds. Historically used to make stone tools due to its conchoidal fracture.

Geological facts

Chalcedony is named after the ancient Byzantine port of Chalcedon. It is a fibrous variety of quartz where the crystals are too small to be seen with a standard microscope.

Field identification & locations

Identify in the field by its waxy luster, translucency, and conchoidal (shell-like) fracture pattern. It will easily scratch glass but cannot be scratched by a steel knife. Common in volcanic regions and river gravels.