mineral

Chalcedony (Agate)

Quartz (Silicon Dioxide, SiO2)

Hardness: 6.5-7 Mohs. Color: Grayish-white to tan with dark inclusions. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.64.

Hardness: 6
Color: Grayish-white to tan with dark inclusions
Luster: Waxy to vitreous

Identified June 30, 2026More mineral →

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Physical properties

Formation & geological history

Forms primarily as secondary deposits in volcanic cavities (vesicles) or sedimentary environments through the deposition of silica-rich fluids. Can be of varied geological ages from Cenozoic to Precambrian.

Uses & applications

Commonly used for lapidary work, jewelry (cabochons), precision bearings, and as tumbling media for collectors.

Geological facts

Chalcedony was highly prized in the ancient world for seals and cylinder stamps because wax would not stick to its smooth, waxy surface.

Field identification & locations

Identified by its waxy luster, translucency, and inability to be scratched by a steel knife. Common in riverbeds and areas with volcanic rock history. Look for smooth, rounded pebbles with a 'milky' or frosted exterior.