sedimentary

Chert (possibly jasper-bearing chert)

Microcrystalline quartz (SiO₂); chert, with iron-oxide staining

AI-generated identification · may be incorrect

Opaque, dark gray-green interior with rusty brown surfaces and a dull to waxy luster; conchoidal-looking fracture. Quartz hardness is about 7 Mohs; no visible cleavage and a microcrystalline structure. Exact identification is limited by the photo.

Identified October 13, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica accumulates and lithifies, commonly replacing carbonate sediments; iron oxides can create reddish-brown patches. Chert occurs in rocks of many geological ages.

Uses & applications

Used historically for tools and fire-starting; attractive patterned pieces may be polished or collected. Common chert generally has modest commercial value.

Geological facts

Chert fractures into sharp edges, making it useful for prehistoric cutting tools. Jasper is an iron-rich, opaque variety of microcrystalline quartz.

Field identification & locations

Look for hardness near 7, a smooth curved fracture, and no grains visible to the naked eye; avoid identifying solely by color. Found worldwide in sedimentary formations; this specimen’s source cannot be determined from the image.