sedimentary

Weathered chert or jasper pebble

Microcrystalline quartz (SiO₂), likely opaque chert/jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; olive-brown and cream mottling, dull to waxy luster, very fine-grained cryptocrystalline structure, and no visible cleavage. The rounded shape and surface staining indicate natural abrasion and weathering.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Chert forms when silica-rich fluids replace or cement fine sediment, commonly in marine limestone or sedimentary layers; jasper is an iron-rich opaque variety. Its exact geological age and locality cannot be determined from the photograph.

Uses & applications

Mostly a collector or teaching specimen; suitable pieces can be polished, cabochon-cut, or used decoratively. Chert was historically important for sharp-edged tools and fire-starting.

Geological facts

A fresh broken surface should be glassy and conchoidally fractured, unlike softer clay-rich rocks. Brown coloration commonly reflects iron oxides or hydroxides.

Field identification & locations

Look for extreme hardness, inability to scratch with a steel knife, and conchoidal fracture; a streak test is usually white to pale. Chert and jasper occur worldwide, especially in sedimentary terrains.