mineral

Agate (or Operculum / Fossil Shell)

Silicon Dioxide (SiO2)

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 →

Explore Agate (or Operculum / Fossil Shell) 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 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.

Other mineral specimens

See all

Sandstone (with potential mineral staining/concretions)

Arenite (SiO2 based)

sedimentary

Schist

Metamorphic

Sandstone with Mineral Veining or Crust

Sedimentary Sandstone (mostly SiO2 with Fe2O3 tinting)

sedimentary

Potassium Feldspar (Orthoclase)

Orthoclase (KAlSi3O8)

mineral

Gypsum (variety Selenite or Alabaster)

Calcium sulfate dihydrate (CaSO4·2H2O)

Mineral

Nephrite Jade

Nephrite

Mineral/Rock