sedimentary

Agate

Silicon dioxide (chalcedony), SiO2

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

Identified November 8, 2026More sedimentary →

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Physical properties

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

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

Widely used in jewelry, decorative ornaments, ornamental carvings, and precision instruments.

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

Identified by its waxy luster and colorful banding; commonly found globally 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)