sedimentary

Chert

Chert (Microcrystalline Quartz, SiO2)

Hardness: 7 on Mohs scale; Color: Grey, tan, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Grey, tan, or brown
Luster: Waxy to dull

Identified June 2, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey, tan, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed by the precipitation of silica in sedimentary environments, often replacing organic material or filling voids in limestone. Can be formed from the accumulation of silica-rich shells of microscopic organisms.

Uses & applications

Historically used for making tools like arrowheads and scrapers due to its sharp edges when broken. Today used as road base, construction aggregate, and occasionally for lapidary work.

Geological facts

Chert is essentially the same material as flint, but 'flint' usually refers to chert found in chalk or limestone modules. It glows when struck with steel (creating sparks) because of its extreme hardness.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is often found as nodules within limestone or as bedded layers in marine sedimentary sequences.