sedimentary

Tumbled brown chert or jasper pebble

Microcrystalline quartz (SiO₂), likely chert/jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque tan-brown with rusty mottling, waxy to dull luster, and conchoidal fractures. Dense, massive, and lacks visible cleavage or individual crystals; the smooth surface appears naturally water-worn or polished.

Identified August 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich fluids replace or cement sediment, often from biogenic silica; jasper is an iron-rich opaque variety. Formation ages range widely from Precambrian to recent, followed by erosion and rounding in streams or beaches.

Uses & applications

Used as decorative stone, cabochons, carvings, lapidary material, and occasionally tools; this ordinary pebble has little commercial value.

Geological facts

The brown coloration commonly comes from iron oxides and hydroxides. Chert can produce very sharp edges when fractured and was widely used for prehistoric cutting tools.

Field identification & locations

Identify it by its glassy/waxy appearance, high hardness, lack of cleavage, dense feel, and inability to scratch it with a steel nail easily; common in gravel beds, river channels, and sedimentary terrains. A definitive chert-versus-jasper identification may require a fresh broken surface or thin section.