sedimentary

Agate

Silicon dioxide (SiO2)

Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, displays distinct concentric color banding, and has a cryptocrystalline structure.

Identified October 18, 2026More sedimentary →

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Physical properties

Hardness of 6.5 to 7 on the Mohs scale, waxy to vitreous luster, displays distinct concentric color banding, and has a cryptocrystalline structure.

Formed by the deposition of silica from groundwater in cavities of igneous and sedimentary rocks over millions of years.

Widely used in jewelry, decorative carvings, precision instruments, and as a popular collector's specimen.

Agate is a variety of chalcedony and was named by the Greek philosopher Theophrastus from the Achates River in Sicily.

Easily identified by its characteristic curved or concentric banding and waxy luster; commonly found worldwide in volcanic rock cavities.

Fossil-bearing concretion, possibly containing a fossil shell or other organic inclusion

Calcareous concretion; exact fossil and host-rock composition are not identifiable from the image

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone or Siltstone

Arenite (if sandstone)

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)