sedimentary

Polished/tumbled yellow-brown chert (likely jasper)

Microcrystalline quartz (chalcedony), SiO₂, iron-oxide colored

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque mustard-yellow to brown, waxy to dull luster, very fine-grained cryptocrystalline structure, no visible cleavage, and conchoidal fracture. The smooth rounded form indicates tumbling or natural abrasion.

Identified September 12, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed when silica-rich groundwater replaced or cemented sediment, with iron oxides producing the ochre color; commonly Paleozoic to Cenozoic, depending on locality. Exact age and provenance cannot be determined from the image.

Uses & applications

Used as an ornamental stone, cabochon, bead, lapidary material, and occasionally aggregate or tool material. Generally inexpensive unless the pattern, locality, or polish is exceptional.

Geological facts

Chert and jasper are varieties of microcrystalline quartz; jasper is typically opaque and impurity-rich. Its fine texture and lack of visible quartz crystals distinguish it from quartzite and coarse-grained rocks.

Field identification & locations

Identify by testing for glass-scratching hardness, examining its waxy surface and conchoidal fractures, and checking for a white streak rather than a metallic one. Common in sedimentary chert beds, gravel deposits, and river cobbles worldwide.