sedimentary

Chert (flint)

Microcrystalline quartz (SiO₂), commonly called chert; brown varieties may be termed brown flint

AI-generated identification · may be incorrect

Opaque brown-gray stone with a waxy to dull luster and sharp, curved conchoidal fracture. Hardness about 7 Mohs; no cleavage; trigonal quartz structure at microscopic scale; specific gravity about 2.6.

Identified October 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica accumulates and recrystallizes in sedimentary settings, often replacing carbonate sediments. Chert occurs in rocks of many geological ages, from ancient Precambrian deposits to modern formations.

Uses & applications

Historically used for tools and fire-starting; today collected and occasionally used in decorative stonework. This unpolished specimen appears to have modest commercial value.

Geological facts

Its sharp fracture edges made flint valuable for prehistoric cutting tools. The image’s brown, glassy-looking fractured surfaces are consistent with chert, though identification from a photo is not definitive.

Field identification & locations

Look for hardness near 7, lack of visible grains, and shell-like fracture; it commonly occurs in limestone, chalk, and gravel deposits worldwide. Approximate value: $1–$10 for a common hand specimen.