sedimentary

Flint or chert fragment

Microcrystalline quartz (SiO₂), commonly termed chert or flint

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark gray to brown, waxy/glassy luster, opaque to slightly translucent edges, and conchoidal fracture without cleavage. The smooth curved fracture surface and fine-grained texture are characteristic.

Identified September 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by replacement or precipitation of microcrystalline quartz in sedimentary rocks, especially limestone and chalk, during diagenesis. Specimen age depends on its host formation; chert occurs from Precambrian to recent deposits.

Uses & applications

Used historically for sharp tools and fire-starting, and today as aggregate, landscaping stone, abrasives, and lapidary material. Attractive patterned pieces may be polished, but this fragment appears ordinary.

Geological facts

Flint is a dark, compact variety of chert, often associated with chalk; the distinction is largely geological and regional rather than mineralogical.

Field identification & locations

Identify by testing for glass-like conchoidal fracture, lack of visible grains, and ability to scratch window glass; a steel blade usually does not scratch it. Common in limestone, chalk, river gravels, and glacial deposits worldwide.