sedimentary

Flint

Microcrystalline quartz (SiO2)

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

Identified August 1, 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 through the accumulation of siliceous skeletal remains of microscopic marine organisms in deep marine environments over millions of years

Uses & applications

Historically used for making stone tools, weapons, and fire-starting flint-and-steel sets; currently used for decorative landscaping, gravel, and abrasive grinding

Geological facts

Flint and chert are fundamentally the same material, though 'flint' typically refers to the dark varieties found in chalk deposits. It was one of the most critical materials for early human technological development due to its ability to fracture into extremely sharp edges

Field identification & locations

Easily identified by its characteristic conchoidal fracture, waxy luster, and high hardness that easily scratches glass. Commonly found weathering out of chalk or limestone cliffs and stream beds worldwide