sedimentary

Agate

Silicon dioxide (Chalcedony), SiO2

Hardness of 6.5 to 7 on the Mohs scale, waxy luster, microcrystalline crystal structure, and a conchoidal fracture with 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 luster, microcrystalline crystal structure, and a conchoidal fracture with distinct concentric banding.

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

Widely used in ornamental jewelry, carved decorative objects, and precision laboratory instruments.

Agate is one of the most popular materials used in lapidary arts and was historically used to make ancient amulets and seals.

Easily identified by its characteristic curved or concentric color bands and waxy sheen; commonly found in river gravels and volcanic regions.

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)