sedimentary

Agate

Cryptocrystalline Quartz (SiO2)

Hardness: 6.5-7 on the Mohs scale; Color: White, grey, and tan bands; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific Gravity: 2.58–2.64

Hardness: 6
Color: White, grey, and tan bands
Luster: Waxy to vitreous

Identified July 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Agate forms through the deposition of silica from groundwater in the cavities of igneous rocks, particularly volcanic lavas, or in sedimentary environments. Its distinct banding represents different cycles of mineral precipitation.

Uses & applications

Commonly used for lapidary arts, jewelry (cabochons), ornamental carvings, and industrially for mortar and pestles due to its hardness and resistance to chemicals.

Geological facts

The name 'agate' comes from the Achates River in Sicily, now known as the Dirillo River, where the stones were first found in ancient times. It is the birthstone for September and symbol of the 12th wedding anniversary.

Field identification & locations

Identified by its waxy luster, translucency, and fine, concentric banding. Collectors should look in river beds, gravel pits, and near volcanic outcrops. It is commonly found in Brazil, India, and the United States (Lake Superior region).