sedimentary

Tumbled chert or flint

Microcrystalline quartz (SiO₂), commonly chalcedony with possible iron-oxide inclusions

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark gray-brown to black, waxy to dull luster, cryptocrystalline structure, conchoidal fracture, and no visible cleavage. The rounded surface appears naturally weathered or tumbled, with reddish-brown iron staining.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or fills cavities in limestone and other sediments, usually as nodules or layers. Chert occurs from Precambrian to recent geological ages and is widespread in sedimentary basins.

Uses & applications

Used historically for sharp tools and fire-starting, and today for archaeological study, lapidary cabochons, décor, and inexpensive specimen collecting.

Geological facts

Freshly broken chert produces very sharp conchoidal edges and may spark against steel; flint is a dark, compact variety of chert. The image may also show minor chalcedony or jasper mixed into the specimen.

Field identification & locations

Identify it by its glassy-waxy appearance, lack of cleavage, very hard surface, and conchoidal fracture; it should scratch ordinary glass. Common sources include chalk and limestone regions, river gravels, and deserts.