sedimentary

Agate

Silicon dioxide (SiO2)

Mohs hardness of 6.5 to 7, vitreous to waxy luster, microcrystalline quartz structure, conchoidal fracture, specific gravity of 2.6

Identified October 19, 2026More sedimentary →

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Physical properties

Mohs hardness of 6.5 to 7, vitreous to waxy luster, microcrystalline quartz structure, conchoidal fracture, specific gravity of 2.6

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

Used primarily in lapidary arts, ornamental carvings, jewelry, and as collector specimens

Agate bands represent successive layers of microscopic quartz crystals deposited inside ancient gas cavities in volcanic rock

Identified by its distinctive concentric banding and waxy luster; commonly found globally in volcanic rock cavities and river gravels

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)