sedimentary

Flint (chert)

Microcrystalline quartz, SiO₂

AI-generated identification · may be incorrect

Dark brown, opaque to slightly translucent at thin edges, with a dull-to-waxy luster and irregular, shell-like conchoidal fracture. Hardness is about 7 Mohs; no visible cleavage; crystals are microscopic and trigonal quartz.

Identified October 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich material replaces or accumulates in sediment, commonly as nodules in limestone or chalk. It can form across many geological ages; the specimen’s age cannot be determined from the image.

Uses & applications

Historically used for tools, blades, and fire-starting; today it is mainly collected or used decoratively.

Geological facts

Flint can produce very sharp edges when fractured and was an important prehistoric tool material.

Field identification & locations

Look for dense, fine-grained stone with sharp conchoidal breaks and often a pale weathered cortex. Chert occurs worldwide in sedimentary rocks; this small, common fragment is typically worth about $1–$10.