sedimentary

Weathered chert or siliceous iron-rich rock

Microcrystalline quartz (SiO₂), possibly ferruginous chert/jasper

AI-generated identification · may be incorrect

Hardness about 6.5–7 Mohs; opaque tan, brown, gray, and rusty-red coloration; dull to slightly waxy luster with a fine-grained, cryptocrystalline texture. It appears massive, lacks visible cleavage, and breaks along irregular to conchoidal fractures; iron oxides cause the reddish-brown zones.

Identified September 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Likely formed when silica-rich groundwater replaced or cemented sediment, with later iron-oxide staining and surface weathering; exact age cannot be determined from the photograph. Chert occurs in sedimentary sequences from Precambrian to recent geological periods.

Uses & applications

Used for tools, abrasives, aggregate, and occasionally ornamental specimens; attractive jasper-like pieces may be polished, but this sample appears mainly a field specimen.

Geological facts

A steel file should barely scratch it, while it can scratch ordinary glass; it may produce a sharp edge when fractured. The granular tan matrix and rusty seams suggest weathered ferruginous chert rather than a crystalline quartz vein.

Field identification & locations

Common in limestone and other sedimentary terrains, including regions worldwide; identify by its very high hardness, lack of cleavage, waxy appearance, and conchoidal fracture. A definitive identification would require a fresh surface, streak, acid test, and perhaps thin-section or XRF analysis.