sedimentary

Flint / Chert

Silicon dioxide (SiO2)

Hardness: 7 on the Mohs scale. Color: Dark gray, brown, or black. Luster: Waxy to vitreous. Crystal structure: Microcrystalline quartz (chalcedony). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 - 2.65.

Hardness: 7 on the Mohs scale
Color: Dark gray, brown, or black
Luster: Waxy to vitreous

Identified August 2, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by the replacement of calcium carbonate by silica in limestone or chalk during diagenesis, or through the accumulation of siliceous skeletal remains of marine organisms over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and spark generation in firearms. Currently used as an abrasive, in road construction, and by collectors.

Geological facts

Flint was one of the earliest materials manipulated by early humans for toolmaking due to its predictable conchoidal fracture, allowing sharp edges to be crafted easily.

Field identification & locations

Identified by its dark color, smooth or waxy feel, conchoidal fracture surfaces, and high hardness capable of scratching glass and producing sparks with steel. Commonly found in chalk and limestone formations worldwide.