sedimentary

Flint Nodule

Microcrystalline Quartz (SiO2)

Mohs hardness of 7, dark grey to black interior with a white chalky cortex, waxy to dull luster, cryptocrystalline structure, conchoidal fracture.

Identified November 14, 2026More sedimentary →

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Physical properties

Mohs hardness of 7, dark grey to black interior with a white chalky cortex, waxy to dull luster, cryptocrystalline structure, conchoidal fracture.

Formed through the replacement of calcium carbonate by silica-rich groundwater within chalk or limestone formations during the Cretaceous period.

Historically used for prehistoric stone tools, weapons, and fire-starting; currently collected as a geological specimen.

Flint produces sparks when struck against steel due to its extreme hardness, making it vital for historical fire-making flintlock mechanisms.

Easily identified by its conchoidal fracture and chalky outer rind, commonly found weathering out of chalk cliffs and limestone beds 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

Sandstone or Siltstone

Arenite (if sandstone)

Fossiliferous Sedimentary Rock

Sedimentary limestone with invertebrate fossil imprint

Shale

Fissile Sedimentary Rock

Sandstone

Arenite

Shale

Clastic sedimentary rock