mineral

Chalcedony (Agate/Chert variety)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: Translucent white to bluish-grey with opaque inclusions; Luster: Waxy to vitreous; Crystal structure: Trigonal/Monoclinic (Cryptocrystalline); Cleavage: None (Conchoidal fracture); Specific gravity: 2.6-2.64.

Hardness: 6
Color: Translucent white to bluish-grey with opaque inclusions
Luster: Waxy to vitreous

Identified June 29, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater in cavities or veins within volcanic or sedimentary rocks. It typically forms at relatively low temperatures and can be found in a wide variety of geological ages.

Uses & applications

Primarily used for lapidary work, jewelry (beads, cabochons), and as a collector's specimen. Historically used for making flint tools and seals.

Geological facts

Chalcedony is made of microcrystalline quartz and moganite. While it looks like common rock, its waxy translucency makes it a bridge between common chert and semi-precious agate.

Field identification & locations

Identify by its waxy luster, translucency when held to light, and smooth conchoidal (shell-like) fracture edges. Commonly found in riverbeds, desert pavements, and volcanic regions worldwide.

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