sedimentary

Flint

Microcrystalline Quartz (SiO2)

Hardness of 7 on the Mohs scale; color typically dark grey, black, brown, or white; waxy to vitreous luster; cryptocrystalline or microcrystalline crystal structure; conchoidal fracture with no cleavage; specific gravity around 2.60 to 2.65.

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions or by the accumulation of siliceous skeletal remains of marine organisms (diatoms, radiolarians) over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and spark-producing fire starters. Currently used in decorative landscaping, road construction, and occasionally for specialized grinding media.

Geological facts

Flint played a vital role in human history during the Stone Age due to its ability to fracture into extremely sharp edges (conchoidal fracture). It was widely used with steel strikers to produce sparks for firearms and fires before the invention of matches.

Field identification & locations

Identified by its distinct waxy luster, conchoidal fracture with sharp edges, and hardness capable of scratching glass. Commonly found as nodules or layers within chalk or limestone formations worldwide.