sedimentary

Flint

SiO2 (Cryptocrystalline Quartz)

Hardness of 7 on the Mohs scale, typically dark grey, brown, or black with a waxy to vitreous luster and conchoidal fracture.

Identified October 17, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, typically dark grey, brown, or black with a waxy to vitreous luster and conchoidal fracture.

Formed as nodules in sedimentary rocks like chalk and limestone through the replacement of calcium carbonate by silica-rich solutions.

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

Flint produces sparks when struck against steel due to its high hardness and microcrystalline structure, making it vital for early human survival.

Easily identified in the field by its distinct conchoidal fracture, sharp edges when broken, and occurrence as nodules within chalk deposits.

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)