sedimentary

Brown flint (chert) fragment

Microcrystalline quartz (SiO₂), chalcedony-rich chert

AI-generated identification · may be incorrect

Hardness about 7 Mohs; dark brown to gray-brown, waxy to dull luster, very fine-grained with no visible crystals or cleavage. The sharp conchoidal fracture and lighter weathered cortex are characteristic.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills pores in limestone and other sediments, commonly during the Cretaceous or younger sedimentary periods. Exact age and locality cannot be determined from the image.

Uses & applications

Historically used for stone tools, fire-starting, and arrowheads; today it is mainly a collector material, lapidary stone, and occasional decorative aggregate.

Geological facts

Flint is a hard variety of chert that commonly occurs as nodules or layers in chalk and limestone. Its conchoidal fracture can produce extremely sharp edges.

Field identification & locations

Identify it by its glassy/waxy appearance, hardness, opaque brown body, and curved shell-like fracture; it should scratch ordinary glass. Common sources include chalk and limestone regions worldwide, including England, France, Texas, Kansas, and the Great Lakes region.