sedimentary

Flint

Sedimentary quartz (Cryptocrystalline silicon dioxide, SiO2)

Mohs hardness of 7, dark gray to black color, waxy to vitreous luster, conchoidal fracture with no cleavage.

Identified November 7, 2026More sedimentary →

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Physical properties

Mohs hardness of 7, dark gray to black color, waxy to vitreous luster, conchoidal fracture with no cleavage.

Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich groundwaters over millions of years.

Historically used for making stone tools and fire-starting flintlock weapons; today utilized in ceramics and abrasive grit.

Flint was one of the earliest materials manipulated by early humans for weaponry and cutting tools due to its predictable sharp fracture.

Identified by its dark color, smooth water-worn surface when found in gravels, and conchoidal break patterns; globally distributed.

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)