sedimentary

Chert (or Flint)

Silicon Dioxide (SiO2)

Hardness of 7 on the Mohs scale; colors range from gray, brown, and yellowish-brown to white and black; waxy to vitreous luster; microcrystalline or cryptocrystalline quartz structure; conchoidal fracture with no true cleavage; specific gravity around 2.60 to 2.65.

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions in marine environments, or through the accumulation of siliceous skeletal remains of microscopic organisms like radiolarians and diatoms over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Modern uses include abrasives, road aggregate, and historically for flintlock firearms.

Geological facts

Chert that is dark or black is commonly referred to as flint. Because of its durability and sharp edges when fractured, it was one of the most valuable materials for early human technology during the Stone Age.

Field identification & locations

Can be identified in the field by its characteristic waxy luster, microcrystalline texture, and sharp conchoidal fracture. It is commonly found embedded as nodules within limestone or chalk formations worldwide.