sedimentary

Iron-rich chert or weathered ironstone

Chert (microcrystalline quartz, SiO₂) with iron-oxide minerals

AI-generated identification · may be incorrect

Brown-gray, opaque, dull to waxy luster with rusty iron staining and a probable conchoidal fracture; quartz hardness about 7, though weathering may soften the surface. Crystal grains are microscopic, with no visible cleavage; specific gravity typically 2.6–3.2 depending on iron content.

Identified September 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely silica-rich sediment or replacement material later hardened and stained by oxidation of iron-bearing minerals. Chert forms in sedimentary environments across many geological ages; the image alone cannot determine its exact age.

Uses & applications

Used historically for sharp-edged tools and occasionally as aggregate or decorative stone; ordinary pieces have little commercial value.

Geological facts

The dark reddish-brown coloration commonly reflects hematite or goethite. A sharp edge and glassy conchoidal fracture are more diagnostic than color alone.

Field identification & locations

Common in sedimentary terrains, including limestone and shale regions; test with a steel file or streak plate, but avoid damage to valuable specimens. It may also be weathered ironstone, which requires a fresh surface or chemical testing for confident identification.