sedimentary

Agate

Silicon Dioxide (Chalcedony), SiO2

Hardness: 6.5 to 7 on the Mohs scale; Color: white, gray, yellowish-brown, and translucent bands; Luster: waxy to vitreous; Crystal structure: microcrystalline/cryptocrystalline (trigonal); Cleavage: none; Specific gravity: 2.58 to 2.64

Hardness: 6
Color: white, gray, yellowish-brown, and translucent bands
Luster: waxy to vitreous

Identified August 1, 2026More sedimentary →

Explore Agate in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed by the deposition of silica from groundwater in the cavities of igneous, metamorphic, or sedimentary rocks, typically in concentric layers over long periods of geological time.

Uses & applications

Used in jewelry, ornamental carvings, decorative objects, and occasionally in industrial applications such as mortars and pestles due to its hardness.

Geological facts

Agates are a variety of chalcedony and often display distinct banding patterns formed by alternating phases of silica deposition under varying chemical conditions.

Field identification & locations

Can be identified in the field by its waxy luster, conchoidal fracture, subtle translucent banding, and resistance to scratching by a steel knife. Commonly found in riverbeds, gravel deposits, and volcanic rock cavities worldwide.