sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 Mohs; Color: dark grey to black; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.8.

Hardness: 6
Color: dark grey to black
Luster: waxy to dull

Identified June 27, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: dark grey to black; Luster: waxy to dull; Crystal Structure: Cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.5-2.8.

Formation & geological history

Formed primarily in marine environments where microcrystalline silica precipitates from water or replaces other minerals in limestone/chalk beds. It can be found in strata dating from the Precambrian to recent times.

Uses & applications

Historically used for stone tools and weapons (arrowheads/scrapers); currently used for road surfacing, as flint in lighters, and occasionally in jewelry as lapidary material.

Geological facts

Flint was a vital resource for prehistoric humans due to its ability to be knapped into sharp edges. It is also famous for its role in 'flintlock' firearms where it strikes steel to produce sparks.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is commonly found as nodules or layers within limestone and chalk formations worldwide.