sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Brown, tan, yellowish-brown, white. Luster: Waxy to vitreous. Crystal structure: Microcrystalline or cryptocrystalline quartz (chalcedony). Cleavage: None, exhibits distinctive conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on the Mohs scale
Color: Brown, tan, yellowish-brown, white
Luster: Waxy to vitreous

Identified July 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through chemical sedimentary processes, typically by the replacement of calcium carbonate in limestone or chalk by silica-rich solutions, or through the direct precipitation of silica from seawater, occurring over millions of years in marine environments.

Uses & applications

Historically used extensively by ancient humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Today used in decorative landscaping, road construction, and occasionally in abrasives or specialized milling.

Geological facts

Chert and flint are essentially the same material, with 'flint' typically reserved for the darker varieties found in chalk formations. Its ability to create sparks when struck against steel made it invaluable for early firearms and fire starting.

Field identification & locations

Easily identified in the field by its waxy luster, hardness (scratches glass easily), and characteristic smooth, curved conchoidal fracture surfaces. Commonly found weathering out of limestone or chalk deposits globally.