sedimentary

Chert / Flint

Silicon Dioxide (Microcrystalline Quartz, SiO2)

Hardness: 7 on the Mohs scale, Color: White, grey, yellowish-brown, brown, or black, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline / Cryptocrystalline (chalcedony), Cleavage: Conchoidal fracture with sharp edges, Specific Gravity: 2.60 to 2.65

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of calcium carbonate in limestone or chalk by silica-rich solutions in deep marine environments over millions of years during the Mesozoic and Cenozoic eras.

Uses & applications

Historically used by early humans for making stone tools, arrowheads, and blades due to its conchoidal fracture. Today used occasionally in decorative landscaping, road aggregate, and grinding mills.

Geological facts

Chert that is dark grey or black is commonly referred to as flint. Flint was historically vital for starting fires when struck against steel, producing a spark.

Field identification & locations

Can be identified in the field by its smooth, waxy surface, characteristic conchoidal fracture, and extreme hardness which easily scratches glass. Commonly found weathering out of limestone or chalk formations worldwide.

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