sedimentary

Iron-rich chert (jasper/chalcedony)

Microcrystalline quartz, SiO₂, variably stained by iron oxides and hydroxides

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; dark brown, black, rust-red, and blue-gray coloration; waxy to dull luster; cryptocrystalline quartz with conchoidal fracture and no cleavage. The rough, weathered surface suggests a natural or minimally worked nodule.

Identified August 19, 2026More sedimentary →

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Physical properties

Formation & geological history

Typically forms when silica-rich groundwater replaces or fills cavities in sedimentary rocks, with later iron staining during weathering; commonly Precambrian to younger, depending on the host formation.

Uses & applications

Used as an ornamental stone, lapidary material, cabochons, and occasionally aggregate. Its dark patterned appearance can make it desirable to collectors, though quality varies greatly.

Geological facts

The blue-gray areas may reflect reduced iron minerals or included clay, while orange-brown zones are likely limonite/goethite. A steel file should barely scratch it; streak testing is less useful because quartz is very hard.

Field identification & locations

Common in weathered sedimentary terrains, volcanic cavities, and iron-rich gravels worldwide. Confirm with a hardness test, conchoidal fracture, and lack of fizz in dilute acid; exact identification requires a fresh surface or laboratory analysis.