sedimentary

Flint or chert

Microcrystalline quartz (SiO₂), commonly called flint when dark and nodular

AI-generated identification · may be incorrect

Hardness about 7 Mohs; dark gray to black, dull to waxy luster, very fine-grained cryptocrystalline structure, no visible cleavage, conchoidal fracture, and white/tan weathering cortex. The sharp curved edges and uniform texture are characteristic of chert.

Identified August 10, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms mainly by replacement of limestone or accumulation of siliceous microfossils in marine sediments, then lithifies during burial. Its exact geological age cannot be determined from the image; chert occurs from Precambrian rocks through modern sedimentary sequences.

Uses & applications

Historically used for stone tools, arrowheads, fire-starting, and cutting edges; today it is mainly a teaching, lapidary, and collectible material, with limited aggregate use.

Geological facts

Flint fractures into extremely sharp edges and can produce sparks against steel. The specimen may be a worked or naturally broken fragment, but the image alone cannot establish human modification.

Field identification & locations

Identify it by hardness, glasslike conchoidal fracture, opaque dark color, and inability to scratch it with a steel knife; it commonly occurs as nodules or beds in limestone and chalk. Common localities include England, France, Texas, Kansas, and many other sedimentary regions.