mineral

Chalcedony (Agate/Carnelian variety)

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Translucent white to milky with orange-brown iron staining; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None; Specific Gravity: 2.6-2.64.

Hardness: 6
Color: Translucent white to milky with orange-brown iron staining
Luster: Waxy to vitreous

Identified May 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed via the deposition of silica from groundwater in cavities of igneous or sedimentary rocks, often occurring in volcanic pockets (amygdules) as late-stage hydrothermal precipitates.

Uses & applications

Used extensively in lapidary work, jewelry (beads and cabochons), ornamental carvings, and industrially for precision bearings and mortars/pestles due to its toughness.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen with a normal microscope. It was a prized material in the ancient world for seals and talismans.

Field identification & locations

Identified in the field by its waxy luster, conchoidal (shell-like) fracture, and translucent edges. Commonly found in riverbeds, desert pavements, and volcanic regions globally.

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