sedimentary

Iron-stained chert (likely)

Microcrystalline quartz (SiO₂), with iron-oxide staining

AI-generated identification · may be incorrect

Opaque, mottled brown-gray, dull to slightly waxy surface, and irregular conchoidal-looking breaks; quartz hardness is about 7 Mohs. The photo does not show enough detail to confirm texture or composition definitively.

Identified October 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica precipitates or accumulates and becomes cemented in sedimentary settings; iron oxides can stain it brown. Its age cannot be determined from the image.

Uses & applications

Chert has historically been used for tools and fire-starting; attractive pieces may be collected or fashioned into small ornaments.

Geological facts

Chert is very fine-grained, so individual quartz crystals are generally invisible to the naked eye.

Field identification & locations

Look for a hard, dense piece with a smooth, curved fracture and no visible grains; similar-looking ironstone or weathered rock is also possible. Chert occurs in sedimentary formations worldwide.