mineral

Chalcedony (Common Agate)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 on the Mohs scale; Color: Translucent white to light gray; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (hexagonal system); Cleavage: None; Fracture: Conchoidal.

Hardness: 6
Color: Translucent white to light gray
Luster: Waxy to vitreous

Identified July 14, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on the Mohs scale; Color: Translucent white to light gray; Luster: Waxy to vitreous; Crystal structure: Cryptocrystalline (hexagonal system); Cleavage: None; Fracture: Conchoidal.

Formation & geological history

Forms from the deposition of silica-rich groundwater in cavities of igneous rocks or through sedimentary replacement of organic materials. Found in volcanic environments and river beds worldwide.

Uses & applications

Used primarily in lapidary work for cabochons, beads, and carvings. Also historically used for making seals, mortars and pestles, and as a semi-precious gemstone in jewelry.

Geological facts

Chalcedony is the cryptocrystalline form of quartz, meaning its crystals are too small to be seen with a standard microscope. It has been used by humans for toolmaking and ornamentation since the Bronze Age.

Field identification & locations

Identify by its waxy luster, translucency, and inability to be scratched by a steel knife. Common in volcanic regions and river gravels. Collectors should look for smoothness and light passing through the edge.