sedimentary

Flint

Microcrystalline Quartz (SiO2)

Hardness of 7 on the Mohs scale, typically dark grey to black in color, waxy to vitreous luster, and exhibits conchoidal fracture.

Identified November 6, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, typically dark grey to black in color, waxy to vitreous luster, and exhibits conchoidal fracture.

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 sparking fire; today used in ceramics and occasionally as a decorative stone.

Flint played a crucial role in human technological development due to its ability to be chipped into extremely sharp edges.

Easily identified by its conchoidal fracture and high hardness that readily scratches glass; commonly found in chalk deposits 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

Sandstone

Arenite

Shale

Shale (clastic sedimentary rock)

Shale (or Mudstone/Siltstone)

Sedimentary Mudrock (SiO2, Al2O3 base with clay minerals)