sedimentary

Flint Nodule

Cryptocrystalline Quartz (SiO2)

Hardness of 7 on Mohs scale, earthy or waxy luster, concoidal fracture, colors range from gray, brown, to yellowish-white with a chalky cortex.

Identified November 7, 2026More sedimentary →

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Physical properties

Hardness of 7 on Mohs scale, earthy or waxy luster, concoidal fracture, colors range from gray, brown, to yellowish-white with a chalky cortex.

Formed diagenetically through the replacement of calcium carbonate in chalk or limestone by silica-rich solutions during the Cretaceous period.

Historically used for prehistoric stone tools and fire-starting; currently valued by collectors and knappers.

Flint is extremely durable and breaks with razor-sharp edges, making it the primary material for ancient weaponry and tools.

Found embedded within chalk or limestone formations; identified by its distinctive conchoidal fracture and soft outer chalky rind.

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)