sedimentary

Agate

Silicon dioxide (Chalcedony), SiO2

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

Identified November 11, 2026More sedimentary →

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Physical properties

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

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

Widely used in ornamental jewelry, decorative carvings, and precision instruments due to its durability.

Agate was highly valued in antiquity as a talisman and for making ornate seals and vessels by ancient Greeks and Romans.

Found worldwide in volcanic rock cavities, easily identified in the field by its concentric color bands and waxy sheen on broken surfaces.

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

Sandstone or Siltstone

Arenite (if sandstone)

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)