mineral

Agate (or Operculum / Fossil Shell)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale; Color: Yellowish-brown, amber, tan with concentric banding; Luster: Waxy to vitreous; Crystal structure: Microcrystalline (trigonal); Cleavage: None, exhibits conchoidal fracture.

Hardness: 6
Color: Yellowish-brown, amber, tan with concentric banding
Luster: Waxy to vitreous

Identified July 23, 2026More mineral →

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Physical properties

Formation & geological history

Formed through the deposition of silica from groundwater solution into cavities within igneous rocks or sedimentary host rocks, creating characteristic concentric bands.

Uses & applications

Used primarily in lapidary arts, jewelry making, decorative crafts, and as a popular collectible specimen.

Geological facts

Agates are famous for their unique, individual banding patterns. Some small disc-like, banded specimens found in rivers or beaches are nicknamed 'eye agates' or are sea snail operculums (trapdoors) petrified into chalcedony.

Field identification & locations

Look for distinct translucent concentric rings and a smooth, waxy surface when wet. Commonly found along gravel beds, riverbanks, lake shores, and beach deposits in volcanic terrains worldwide.