sedimentary

Polished brown chert or jasper pebble

Microcrystalline quartz (SiO₂), likely ferruginous chert/jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; brown to reddish-brown, opaque, with a dull-to-waxy luster and no visible crystal cleavage. Dense, fine-grained, rounded and surface-smoothed, likely by tumbling or natural abrasion.

Identified September 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich fluids replace or cement fine sediments, with iron oxides producing the brown coloration; commonly Paleozoic to younger, though exact age cannot be determined visually. The rounded shape indicates stream, beach, or lapidary abrasion.

Uses & applications

Used for cabochons, beads, polished stones, carving, and decorative objects; chert was historically important for sharp-edged tools and fire-starting.

Geological facts

Jasper is an opaque, impure variety of microcrystalline quartz, while chert is often more uniformly silica-rich; the boundary between them is gradual. The pale streaks may reflect silica-rich veins, weathering, or included mineral material.

Field identification & locations

Identify by its very fine texture, high hardness, opaque brown color, waxy polish, and inability to scratch with a steel knife easily; a streak test should be white to pale brown. Common in sedimentary terrains, gravel beds, river channels, and beaches.