mineral

Chalcedony

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: Grayish-white, translucent; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.64.

Hardness: 6
Color: Grayish-white, translucent
Luster: Waxy to dull

Identified April 2, 2026More mineral →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Grayish-white, translucent; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None; Specific gravity: 2.6-2.64.

Formation & geological history

Formed from the deposition of silica-rich water in volcanic cavities (geodes) or sedimentary layers at low temperatures. It can also form by the replacement of organic materials like wood.

Uses & applications

Used in jewelry (cabochons, beads), decorative carvings, and as a semi-precious gemstone. Also used historically for weapon tips and seals due to its toughness.

Geological facts

Chalcedony is the umbrella term for various cryptocrystalline quartzes including agate, onyx, and jasper. Its name is derived from the ancient Greek town of Chalkedon in Asia Minor.

Field identification & locations

Identify in the field by its waxy luster, conchoidal (shell-like) fracture, and inability to be scratched by a steel knife. It is frequently found in riverbeds or areas with volcanic rock outcrops.