sedimentary

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5-7 on the Mohs scale; Color: Variable, often banded in grey, white, blue, brown, or red; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline quartz)

Hardness: 6
Color: Variable, often banded in grey, white, blue, brown, or red
Luster: Waxy to vitreous

Identified August 4, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 on the Mohs scale; Color: Variable, often banded in grey, white, blue, brown, or red; Luster: Waxy to vitreous; Crystal Structure: Trigonal (microcrystalline quartz)

Formation & geological history

Formed by the deposition of silica from groundwater in the cavities of igneous or sedimentary rocks, often developing concentric bands over millions of years.

Uses & applications

Used in jewelry, ornaments, lapidary art, mortar and pestle sets, and as a popular collector's specimen.

Geological facts

Agates were named by the ancient Greek philosopher Theophrastus, who discovered the stone along the shoreline of the Achates River in Sicily.

Field identification & locations

Can be identified by its distinctive concentric banding, waxy luster, and conchoidal fracture. Commonly found in volcanic rock cavities worldwide, particularly in Brazil, Uruguay, and parts of the United States.