gemstone

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale; Color: Varies widely including brown, white, red, gray, pink, black, and yellow with distinctive concentric banding; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline quartz)

Hardness: 6
Luster: Waxy to vitreous

Identified July 31, 2026More gemstone →

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Physical properties

Formation & geological history

Formed by the deposition of silica from groundwater in the cavities of igneous and sedimentary rocks, typically over millions of years.

Uses & applications

Used primarily in jewelry, ornamental carvings, decorative objects, and historically for precision instruments like mortar and pestles due to its hardness.

Geological facts

Agate was named by Theophrastus, a Greek philosopher and naturalist, who discovered the stone along the shoreline of the Achates River in Sicily.

Field identification & locations

Easily identified by its distinct concentric color bands and waxy luster. Commonly found worldwide, notably in Brazil, Uruguay, India, and parts of the United States like Oregon and Lake Superior.