sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 Mohs. Color: Black to dark grey. Luster: Waxy to vitreous. Structure: Microcrystalline/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.91.

Hardness: 6
Color: Black to dark grey
Luster: Waxy to vitreous

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs. Color: Black to dark grey. Luster: Waxy to vitreous. Structure: Microcrystalline/Cryptocrystalline. Cleavage: None (conchoidal fracture). Specific Gravity: 2.58-2.91.

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often replacing organic material or filling cavities in limestone/chalk. Found in nodules or bedded deposits throughout the geologic record from the Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (knapping) and starting fires (flint and steel). Modern uses include gemstones (jasper/agate varieties), road surfacing, and industrial grinding media.

Geological facts

Flint was one of the most important resources for prehistoric humans due to its ability to break into sharp edges. It is chemically identical to quartz but has a different internal crystal structure.

Field identification & locations

Identify by its 'shell-like' conchoidal fracture, waxy feel, and ability to scratch glass. Often found in chalk cliffs or as nodules in limestone fields.