sedimentary

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale. Color: Variable, often banded with white, grey, brown, orange, and yellow. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline quartz). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.58 to 2.64.

Hardness: 6
Luster: Waxy to vitreous

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms primarily within the cavities of volcanic and metamorphic rocks through the deposition of silica from groundwater solutions, often in concentric bands around a core. Can range from millions to billions of years in geological age.

Uses & applications

Widely used in jewelry, ornamental carvings, polished specimens for collectors, and historically for precision instruments like mortar and pestles.

Geological facts

Agate is one of the most popular and varied forms of chalcedony. The name comes from the Achates River in Sicily, where agates were found in antiquity.

Field identification & locations

Easily identified by its characteristic concentric color banding and waxy luster. Commonly found in stream beds, gravel deposits, and volcanic regions worldwide. Collectors look for smooth, water-worn pebbles along shores and riverbanks.