mineral

Chalcedony/Agate

Cryptocrystalline Silica (SiO2)

Hardness: 6.5-7 on Mohs scale; Color: honey-brown to tan; Luster: waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: none; Fracture: Conchoidal; Specific Gravity: 2.6

Hardness: 6
Color: honey-brown to tan
Luster: waxy to vitreous

Identified July 19, 2026More mineral →

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Physical properties

Hardness: 6.5-7 on Mohs scale; Color: honey-brown to tan; Luster: waxy to vitreous; Crystal structure: Trigonal (microscopic); Cleavage: none; Fracture: Conchoidal; Specific Gravity: 2.6

Formation & geological history

Formed via precipitation of silica-rich fluids in volcanic or sedimentary cavities. This waterworn specimen likely originated from weathered igneous rock and was transported by river or glacial action.

Uses & applications

Used for lapidary work, jewelry, tumbling, and as a collector's specimen. Chalcedony is also used industrially in precision bearings.

Geological facts

Chalcedony is a cryptocrystalline form of silica, meaning its crystals are too small to be seen without high magnification. When semi-translucent and brownish, it is often referred to as carnelian or sard.

Field identification & locations

Check for translucency when held to a light source and a waxy surface texture. Commonly found in riverbeds, gravel pits, and coastal areas throughout the world.