sedimentary

Polished brown chert or jasper pebble

Microcrystalline quartz (SiO₂), likely chert/jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown, tan, and cream coloration with a smooth, waxy-to-dull luster. It is composed of cryptocrystalline quartz, lacks visible cleavage, and commonly has conchoidal fracture; the surface appears naturally water-worn or polished.

Identified September 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich material replaces or accumulates within sediment, often during diagenesis; jasper is an opaque, iron-stained variety. Formation ages range from Precambrian to recent, while the rounded shape likely reflects stream or beach transport.

Uses & applications

Used for ornamental objects, cabochons, beads, carvings, and historically for cutting tools; attractive jasper/chert specimens have modest collector value.

Geological facts

Chert can preserve microscopic fossils and may occur as nodules or beds in limestone and other sedimentary rocks. Iron oxides produce the characteristic reddish-brown coloration.

Field identification & locations

Identify it by its very fine texture, opaque appearance, lack of cleavage, hardness, and conchoidal fracture; it should scratch glass but not be scratched by steel. Common worldwide, especially in gravel deposits, limestone regions, and volcanic-sedimentary terrains.