sedimentary

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5-7 on the Mohs scale; Color: varies widely including white, grey, blue, yellow, orange, and brown; Luster: waxy to vitreous; Crystal structure: microcrystalline quartz (trigonal); Cleavage: none; Specific gravity: 2.58-2.64

Hardness: 6
Luster: waxy to vitreous

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed mainly in cavities of volcanic and metamorphic rocks through the deposition of silica-rich groundwater solutions in concentric layers over millions of years.

Uses & applications

Used for ornamental objects, jewelry, decorative carvings, and as a popular specimen for rock collectors.

Geological facts

Agates are often found in ancient lava flows, where gas bubbles left empty cavities that eventually filled with silica deposits. The bands in an agate reflect changes in the water's mineral content and deposition conditions over time.

Field identification & locations

Easily identified by its waxy luster, conchoidal fracture, and characteristic concentric banding or translucent areas. Commonly found in riverbeds, lake shores, and gravel pits worldwide, especially in regions with volcanic history.