sedimentary

Chert (Flint / Jasper / Hornstone)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Tan, beige, brown, yellow-orange iron staining with dark gray/black manganese or organic inclusions; Luster: Waxy to dull; Cleavage: None (exhibits prominent conchoidal fracture); Specific gravity: ~2.65

Hardness: 7 on Mohs scale
Luster: Waxy to dull

Identified July 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as chemical precipitates or biogenic deposits from silica-rich fluids in marine or freshwater sedimentary environments. Silica accumulates as gel-like precipitates or replaces carbonate minerals like limestone and dolomite.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-striking flints. Modern uses include road aggregate, landscape stone, and lapidary work for cabochons and decorative specimens.

Geological facts

Chert was one of the earliest rocks utilized by prehistoric humans due to its ability to produce extremely sharp, glass-like edges when fractured (knapped). Iron oxides give it yellow and red tones, while manganese oxides create dark dendritic patterns.

Field identification & locations

Identify in the field by its distinct smooth, shell-like (conchoidal) fracture surfaces, sharp edges when broken, and inability to be scratched by a steel pocket knife. Widespread in limestone and dolomite formations worldwide.

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