sedimentary

Flint

Microcrystalline Quartz (SiO2)

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

Identified October 23, 2026More sedimentary →

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Physical properties

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

Formed through the chemical replacement of limestone or chalk by silica-rich groundwater in marine environments over millions of years.

Historically used for making stone tools and fire-starting; currently used in decorative landscaping and occasionally in jewelry.

Flint is a hard variety of the mineral quartz and has been utilized by humans for over two million years to create sharp implements.

Easily identified in the field by its distinct conchoidal fracture and waxy luster; commonly found embedded in chalk or limestone 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)