sedimentary

Flint

Microcrystalline quartz (SiO2)

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

Formed as nodular masses in sedimentary rocks such as chalk or limestone through the replacement of calcium carbonate by silica.

Historically used for making stone tools and fire-starting; currently used in decorative aggregates, ceramics, and abrasives.

Flint was crucial for early human survival due to its ability to hold a sharp edge and strike sparks against iron.

Identify by its dark color, waxy luster, conchoidal fracture, and ability to scratch 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

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)