gemstone

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline crystal structure, conchoidal fracture, specific gravity around 2.60 to 2.65, displays distinctive concentric banding in various colors.

Identified August 5, 2026More gemstone →

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Physical properties

Formation & geological history

Formed primarily within cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions over millions of years.

Uses & applications

Used extensively in jewelry, ornamental carvings, decorative objects, precision instruments, and mortar and pestle sets due to its hardness and durability.

Geological facts

Agate was named by the Greek philosopher Theophrastus after the Achates river in Sicily where the stones were first found.

Field identification & locations

Easily identified by its characteristic layered banding patterns and translucent to opaque appearance. Commonly found worldwide, notably in Brazil, Uruguay, India, and the USA.