sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 6.5-7 (Mohs scale), Color: Dark gray to black, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Hardness: 6

Identified June 27, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale), Color: Dark gray to black, Luster: Waxy to dull, Crystal Structure: Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

Formation & geological history

Formed through the accumulation of silica-rich microfossils (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road surfacing, as grinding media, and for starting fires (striking against steel).

Geological facts

Flint is a variety of chert that occurs primarily in chalk and marly limestone. It was the most important material for technological development during the Stone Age due to its ability to split into thin, sharp splinters.

Field identification & locations

Identify by its characteristic conchoidal fracture (curved, glass-like breaks) and ability to scratch glass. Commonly found in riverbeds, glacial deposits, and embedded in limestone outcrops.