sedimentary

Chert / Flint

Microcrystalline quartz (SiO2)

Hardness of 7 on the Mohs scale, typically grayish-white to dark brown or black in color, waxy to vitreous luster, cryptocrystalline structure, conchoidal fracture with very sharp edges, and a specific gravity of 2.60 to 2.65.

Identified August 7, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the diagenesis of silica-rich deep-marine sediments (such as diatom or radiolarian oozes) or via the replacement of limestone or chalk by silica-rich groundwater. Found across various geological ages from Precambrian to Cenozoic.

Uses & applications

Historically used for making stone tools, arrowheads, and striking fire due to its conchoidal fracture and spark-producing properties when hit against steel. Modern uses include decorative landscaping and abrasive grit.

Geological facts

Chert and flint are chemically identical forms of microcrystalline quartz, though the term 'flint' is often reserved for dark variations found in chalk deposits. Because of its durability and sharp edges, it was one of the most critical materials for early human technology during the Stone Age.

Field identification & locations

Easily identified by its smooth, waxy luster, conchoidal fracture surfaces, and extreme hardness that easily scratches glass. It is commonly found embedded as nodules or bands within limestone and chalk formations worldwide.