sedimentary

Brown chert or jasper fragment

Microcrystalline quartz (SiO₂), likely iron-stained chert/jasper

AI-generated identification · may be incorrect

Opaque brown to tan, waxy-to-dull luster, very fine-grained cryptocrystalline structure, with irregular conchoidal fracture and no visible cleavage; Mohs hardness about 6.5–7, specific gravity roughly 2.6. The glossy surface may indicate polishing or wetting.

Identified August 31, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich groundwater replaces or cements sediment, commonly as nodules or beds in limestone and other sedimentary rocks; iron oxides produce the brown coloration. Chert formation spans much of geological time, from Precambrian to modern deposits.

Uses & applications

Used historically for sharp tools and fire-starting, and today for lapidary cabochons, carvings, decorative stone, and occasionally aggregate.

Geological facts

Jasper is the opaque, impurity-rich variety of chalcedony; chert is the broader fine-grained silica-rock term. A steel file should barely scratch it, while it can scratch ordinary glass.

Field identification & locations

Common in limestone regions, river gravels, and silica-rich sedimentary formations worldwide; look for uniform microtexture, conchoidal edges, and lack of visible grains. Exact identification is uncertain from the photograph alone.