sedimentary

Flint

Silicon dioxide (SiO2)

Hardness of 7 on the Mohs scale, typically dark grey to black or brown, waxy to vitreous luster, and exhibits conchoidal fracture with no cleavage.

Identified October 17, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, typically dark grey to black or brown, waxy to vitreous luster, and exhibits conchoidal fracture with no cleavage.

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

Historically used for making stone tools and fire-starting; currently utilized in abrasives, ceramics, and historical reenactments.

Flint was a crucial material for early human survival due to its ability to be chipped into extremely sharp edges.

Identified easily by its conchoidal fracture and waxy luster, commonly found embedded in chalk and limestone formations 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)