sedimentary

Polished banded chert or jasper

Microcrystalline quartz (chalcedony), SiO₂, with iron-oxide impurities

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque brown, gray, and black horizontal banding; waxy to vitreous luster when polished; massive, with no visible cleavage and conchoidal fracture. Its rounded shape indicates tumbling or natural water wear.

Identified September 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed from silica-rich sediment that recrystallized into microcrystalline quartz, with iron and manganese producing the brown-black bands. Chert and jasper range from Precambrian to recent ages and commonly occur in marine sedimentary beds, nodules, and river gravels.

Uses & applications

Used for lapidary cabochons, carvings, beads, and polished display stones; historically, chert was widely used for cutting tools and fire-starting.

Geological facts

The dark bands may reflect changing sediment chemistry or iron/manganese-rich layers. A glassy conchoidal fracture and inability to scratch it with a steel knife support a chert/jasper identification.

Field identification & locations

Common in sedimentary formations and stream gravels worldwide, including the Great Lakes region, the western United States, Australia, and Europe. Exact identification would benefit from a fresh fracture, streak, and locality information.