sedimentary

Flint or chert nodule

Microcrystalline quartz (chalcedony), SiO₂

AI-generated identification · may be incorrect

Typically dark gray to brown with a waxy-to-dull luster, conchoidal fracture, and no visible crystals; hardness about 6.5–7 Mohs, specific gravity ~2.6, with an irregular pale chalcedony or limestone-like rind visible here.

Identified August 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by silica replacement or precipitation in marine limestone and chalk, commonly during the Cretaceous or other Phanerozoic sedimentary periods; the exact age cannot be determined from the photo.

Uses & applications

Used historically for stone tools and fire-starting, and today for carving, lapidary work, aggregate, and teaching collections; attractive patterned pieces may be sold as specimens.

Geological facts

Flint is generally a dark, compact variety of chert, while chert is the broader geological term. Fresh edges can be extremely sharp because of conchoidal fracture.

Field identification & locations

Common in chalk and limestone regions, including England, France, the American Midwest, Texas, and parts of Australia. Test cautiously for a glassy conchoidal chip and resistance to a steel file; acid testing the pale rind may reveal carbonate matrix.