sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, or rust; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 on Mohs scale
Color: Brown, tan, or rust
Luster: Dull to waxy

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, or rust; Luster: Dull to waxy; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed by the precipitation of silica from sea water or by the replacement of calcium carbonate by silica in limestone environments. Often found as nodules or bedded layers in marine sedimentary rocks dating from the Precambrian to recent eras.

Uses & applications

Historically used for making stone tools (flint) due to its sharp edges when broken. Today, used in construction aggregate, road surfacing, and as a durable material in lapidary work.

Geological facts

Flint is a variety of chert. Because of its hardness and ability to hold a sharp edge, it was one of the most important minerals for early human survival, used for arrowheads and starting fires.

Field identification & locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) breakage patterns. Commonly found in riverbeds, glacial till, and embedded in limestone cliffs.