sedimentary

Weathered iron-rich chert or jasper

Microcrystalline quartz (SiO₂), variably stained by iron oxides such as hematite and goethite

AI-generated identification · may be incorrect

Typically hardness 6.5–7 Mohs, opaque gray-brown to ochre-yellow, with a dull to waxy luster and conchoidal fracture; the yellow-orange zones reflect iron-oxide staining. Crystal structure is cryptocrystalline quartz, with no visible cleavage.

Identified August 16, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms when silica-rich sediment or groundwater replaces or cements rock, while later oxidation produces the rusty colors. It may range from Precambrian to much younger, depending on its geological setting.

Uses & applications

Used historically for cutting tools and occasionally as decorative stone, cabochons, or lapidary material; this ordinary specimen has little commercial value.

Geological facts

Chert and jasper are varieties of microcrystalline quartz; jasper is generally more strongly colored or opaque because of impurities. The sharp, curved fracture surfaces are useful diagnostic clues.

Field identification & locations

Look for a very hard, nonporous stone that scratches glass and breaks with curved, sharp edges; a steel nail should not scratch it. Common in sedimentary formations, river gravels, and iron-rich weathering zones.