sedimentary

Iron-stained chert or siliceous sedimentary rock

Microcrystalline quartz (SiO₂), likely chert with iron-oxide staining

AI-generated identification · may be incorrect

Usually Mohs hardness 6.5–7, dull to waxy luster, gray-brown color with orange-brown limonite/goethite coatings, and no visible cleavage. It commonly breaks with smooth conchoidal fractures; the specimen appears dense and fine-grained.

Identified August 25, 2026More sedimentary →

Explore Iron-stained chert or siliceous sedimentary rock in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Chert forms when silica-rich fluids precipitate microcrystalline quartz, often replacing sediment or accumulating as siliceous beds; the exact geological age cannot be determined from the photograph. Orange-brown areas are weathering products of iron-bearing minerals.

Uses & applications

Used historically for sharp tools and occasionally as aggregate or decorative stone. Ordinary pieces have little commercial or jewelry value, though attractive jasper-like varieties may be collected or polished.

Geological facts

The hard, glassy fracture and very fine texture distinguish chert from many softer mudstones. Iron oxides can produce vivid rust, yellow, and red patterns without making the rock metallic.

Field identification & locations

Test an inconspicuous edge with a steel knife: true chert generally scratches glass and resists the knife. Common occurrences include limestone beds, river gravels, and weathered sedimentary outcrops worldwide.