gemstone

Agate

Silicon dioxide (Chalcedony), SiO2

Hardness of 6.5 to 7 on the Mohs scale, colors range from clear, white, gray, yellow, brown, to red, vitreous to waxy luster, microcrystalline (cryptocrystalline) quartz structure, conchoidal fracture with no true cleavage, specific gravity of 2.58 to 2.64.

Identified July 28, 2026More gemstone →

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Physical properties

Formation & geological history

Formed mainly within cavities of volcanic rocks or ancient lavas through the deposition of silica from groundwater solutions, often in concentric bands over millions of years.

Uses & applications

Used in jewelry, decorative ornaments, gemstone carvings, and historically in precision instruments such as mortar and pestles due to its durability.

Geological facts

Agates are often found lining or filling geodes and are named after the Achates River in Sicily, where they were found in ancient times.

Field identification & locations

Can be identified by its characteristic banded patterns, waxy luster, and translucent to opaque appearance. Commonly found worldwide in gravel beds, stream beds, and volcanic regions.