sedimentary

Chert / Flint

Cryptocrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale; Color: typically cream, beige, or grey (based on image); Luster: waxy to dull; Crystal structure: cryptocrystalline (microscopic crystals); Cleavage: none, exhibits conchoidal (shell-like) fracture; Specific Gravity: 2.65.

Hardness: 7 on the Mohs scale
Color: typically cream, beige, or grey (based on image)
Luster: waxy to dull

Identified March 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from sea water or by the replacement of calcium carbonate (limestone) by silica. It is found in sedimentary strata ranging from the Precambrian to the present day.

Uses & applications

Historically used for making stone tools and arrowheads due to its sharp fracture edges. Modernly used as a decorative stone in landscaping, as an abrasive, and in some construction road ballast.

Geological facts

Because it produces sparks when struck against steel, it was the primary ignition source for flintlock firearms. It is incredibly durable and chemically resistant to weathering.

Field identification & locations

Identify in the field by its smooth, waxy feel and the way it breaks into sharp, curved slices (conchoidal fracture). It often has a white 'rind' or cortex on the outside when found in nodules. Very common in limestone-rich regions.