sedimentary

Flint or chert fragment

Microcrystalline quartz (SiO₂), likely flint/chert

AI-generated identification · may be incorrect

Dark gray-brown, opaque to slightly translucent edges, dull-to-waxy luster, very fine-grained and conchoidally fractured; Mohs hardness about 7, with no visible cleavage. The irregular piece may show a lighter weathered cortex or iron staining.

Identified September 6, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica replaces or precipitates within marine or freshwater sediments, commonly from biogenic silica. It occurs from Precambrian to Recent rocks; the specimen’s age cannot be determined from the photograph.

Uses & applications

Used historically for cutting tools and fire-starting, and today as a lapidary or teaching specimen; attractive pieces may be polished, though this fragment has limited commercial value.

Geological facts

Freshly broken chert produces sharp, curved fracture surfaces and can resemble dark glass, but it is natural silica rather than manufactured glass.

Field identification & locations

Look for extreme hardness, inability to scratch it with a steel knife, a white streak or no obvious streak, and conchoidal fracture. Common locations include limestone beds, chalk, river gravels, and eroded sedimentary terrains worldwide.