sedimentary

Weathered iron-rich chert or jasper

Microcrystalline quartz (SiO₂), commonly colored by iron oxides/hydroxides

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque brown, ochre, gray, and cream with earthy to dull/waxy luster. Typically massive, very fine-grained, and conchoidally fracturing; the rough surface appears strongly weathered and iron-stained.

Identified August 28, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from silica-rich chemical or biogenic sediment that lithified and recrystallized into microcrystalline quartz, later stained by groundwater iron. Its exact geological age cannot be determined from the image; chert occurs from Precambrian to recent formations.

Uses & applications

Used historically for tools and fire-starting, and occasionally as lapidary material, aggregate, or decorative stone. Ordinary weathered pieces generally have little commercial value.

Geological facts

The yellow-brown coloration is characteristic of limonite/goethite staining rather than a separate dominant mineral. It may also be called ferruginous chert or jasper, although jasper is an opaque, iron-rich variety of microcrystalline quartz.

Field identification & locations

Identify it by its very fine texture, lack of visible crystals, high hardness, and sharp/conchoidal fracture; it should scratch glass. Common in sedimentary terrains, river gravels, and weathered iron-rich zones worldwide.