sedimentary

Agate

Silicon dioxide (chalcedony variety), SiO2

Hardness of 6.5-7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, and conchoidal fracture with no cleavage.

Identified November 9, 2026More sedimentary →

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Physical properties

Hardness of 6.5-7 on the Mohs scale, waxy to vitreous luster, cryptocrystalline structure, and conchoidal fracture with no cleavage.

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

Commonly used in ornamental jewelry, decorative carvings, and precision instruments.

Agate is often associated with volcanic rocks and exhibits colorful, concentric bands formed by successive layers of silica deposition.

Identify in the field by its waxy luster, microcrystalline banding, and resistance to weathering; found worldwide.

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)