sedimentary

Chert / Flint

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, typically gray, brown, or white, waxy to vitreous luster, conchoidal fracture with sharp edges, no cleavage, specific gravity around 2.60 to 2.65.

Identified July 31, 2026More sedimentary →

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Physical properties

Hardness of 7 on the Mohs scale, typically gray, brown, or white, waxy to vitreous luster, conchoidal fracture with sharp edges, no cleavage, specific gravity around 2.60 to 2.65.

Formation & geological history

Formed through the replacement of limestone or chalk by silica-rich solutions in deep marine environments, or from the accumulation of siliceous skeletal remains of microscopic organisms over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and spark generation in firearms. Today used in abrasives, road aggregate, and occasionally in lapidary work.

Geological facts

Chert and flint are chemically identical forms of microcrystalline quartz, traditionally separated by color where darker varieties are called flint and lighter ones chert.

Field identification & locations

Easily identified by its distinctive conchoidal fracture and extreme hardness which allows it to scratch glass. Found worldwide in sedimentary rock sequences, particularly within chalk and limestone formations.