sedimentary

Chert

Microcrystalline Quartz (SiO2)

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

Identified August 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed via chemical sedimentary processes, often through the replacement of limestone or chalk by silica-rich solutions, or through the accumulation of siliceous skeletal remains of marine organisms like radiolarians and diatoms over geological timescales.

Uses & applications

Historically used extensively by ancient humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used historically for striking fire, and occasionally in modern aggregate or abrasive applications.

Geological facts

Chert is extremely durable and weather-resistant, which is why ancient stone artifacts made of chert survive in pristine condition for thousands of years. Varieties include flint, jasper, and chalcedony.

Field identification & locations

Can be identified in the field by its characteristic conchoidal fracture, sharp edges when broken, waxy luster, and high hardness that easily scratches glass. Commonly found within chalk or limestone formations worldwide.