sedimentary

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5-7 on the Mohs scale. Color: Yellow, orange, white, and translucent bands. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None (conchoidal fracture). Specific gravity: 2.58-2.64.

Hardness: 6
Color: Yellow, orange, white, and translucent bands
Luster: Waxy to vitreous

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the deposition of silica from groundwater in the cavities of igneous or sedimentary rocks, typically occurring over millions of years in ancient volcanic or hydrothermal environments.

Uses & applications

Used in ornamental objects, jewelry, carvings, and lapidary art, as well as historically for precision instruments like mortar and pestles.

Geological facts

Agate is a variety of chalcedony that typically forms in concentric layers or bands. The coloration depends on trace impurities such as iron, chromium, or manganese present during its formation.

Field identification & locations

Easily identified by its characteristic waxy luster, conchoidal fracture, and distinct fine concentric banding. Commonly found in regions with historical volcanic activity, such as riverbeds and gravel deposits worldwide.