sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Grey, beige, and white with reddish-orange iron staining; Luster: Waxy to dull; Cleavage: None (conchoidal fracture); Crystal Structure: Cryptocrystalline

Hardness: 7 Mohs scale
Color: Grey, beige, and white with reddish-orange iron staining
Luster: Waxy to dull

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Grey, beige, and white with reddish-orange iron staining; Luster: Waxy to dull; Cleavage: None (conchoidal fracture); Crystal Structure: Cryptocrystalline

Formation & geological history

Formed by the precipitation of silica from groundwater in sedimentary environments, often replacing carbonate minerals in limestone or chalk beds. This specimen shows typical oxidation (iron staining) from weathering.

Uses & applications

Historically used for stone tools and starting fires; currently used as construction aggregate, road base, and for some lapidary purposes.

Geological facts

Chert is so hard that it can scratch steel. It was one of the most vital materials for early humans because its conchoidal fracture allows it to be knapped into extremely sharp edges.

Field identification & locations

Identify in the field by its waxy appearance, sharp edges when broken, and inability to be scratched by a steel knife. It is ubiquitous in sedimentary basins worldwide.