sedimentary

Chert / Flint

Silicon Dioxide (SiO2)

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

Hardness: 7 on Mohs scale
Color: Varies from white, grey, brown, to yellowish-tan
Luster: Waxy to vitreous

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of calcium carbonate by silica-rich solutions in sedimentary environments like chalk or limestone, or through the direct precipitation of silica from seawater, occurring across various geological ages primarily in marine deposits.

Uses & applications

Historically used extensively by ancient humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Today used occasionally in decorative landscaping, road aggregate, and historically for fire-starting.

Geological facts

Chert and flint are essentially the same material, though historically 'flint' has been used for darker varieties found in chalk formations. It produces sparks when struck against steel, which made it crucial for early firearms and fire making.

Field identification & locations

Easily identified by its smooth, waxy luster, conchoidal fracture showing concentric ripples, and extreme hardness that easily scratches glass. Found worldwide, particularly in limestone and chalk beds.