sedimentary

Polished/tumbled chert or jasper pebble

Microcrystalline quartz (SiO₂), likely brown jasper/chert

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque tan-brown color with subtle mottling, waxy-to-dull luster, very fine-grained cryptocrystalline structure, and no visible cleavage. Its smooth rounded shape indicates tumbling or prolonged water abrasion.

Identified September 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert and jasper form when silica replaces or precipitates within sedimentary material, often from biogenic silica or silica-rich fluids; individual pieces may range from Paleozoic to younger geological ages. Common sources include river gravels, sedimentary formations, and volcanic-associated silica deposits.

Uses & applications

Used for lapidary cabochons, beads, carvings, and ornamental stones; historically, chert was widely knapped for tools. Ordinary tumbled pieces have modest decorative value.

Geological facts

Jasper is an opaque, impurity-rich variety of microcrystalline quartz, whereas relatively uniform fine-grained material is commonly called chert. Brown coloration typically comes from iron oxides or hydroxides.

Field identification & locations

Identify it by its opaque appearance, smooth waxy surface, quartz-like hardness, and inability to scratch it with a steel knife easily; a streak test is usually white to pale. Commonly found in riverbeds and sedimentary or volcanic terrains.