sedimentary

Flint or chert

Microcrystalline quartz (SiO₂), likely gray chert/flint

AI-generated identification · may be incorrect

Hardness about 7 Mohs; dark gray to bluish-gray, waxy to dull luster, very fine-grained cryptocrystalline structure, no visible cleavage, and conchoidal fracture. The specimen appears naturally fractured or roughly knapped, with a lighter weathered cortex.

Identified September 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica replaces or accumulates within marine or freshwater sediment, commonly from biogenic silica. It can range from Paleozoic to Cenozoic in age; the image alone cannot establish a precise age or locality.

Uses & applications

Used historically for sharp tools and fire-starting, and occasionally as aggregate or decorative stone. Attractive pieces have modest collector value.

Geological facts

Chert and flint are mineralogically similar; “flint” generally refers to dark chert, especially nodules associated with chalk. Its conchoidal fracture can produce razor-sharp edges.

Field identification & locations

Identify by testing for glass-scratching hardness, observing conchoidal fracture, and distinguishing it from glass by its natural cortex and opaque, fine-grained interior. Common in limestone, chalk, river gravels, and glacial deposits.