sedimentary

Chert (Iron-stained)

Microcrystalline or cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 on Mohs scale (scratches glass); Color: Mottled red, brown, white, and black due to iron and manganese oxides; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.

Hardness: 6
Luster: Waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich biogenic remains (like diatoms or radiolarians) or the chemical replacement of limestone/dolomite by silica-rich fluids. Can be found in geological formations ranging from the Precambrian to the present.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modernly used as a decorative stone, in construction aggregate, or for lapidary tumbling and jewelry.

Geological facts

Chert is so hard and dense that it was commonly used as 'flint' to start fires when struck against steel. The reddish hue in this specimen is specifically caused by hematite (iron oxide) impurities.

Field identification & locations

Identify in the field by its hardness (it should not be scratchable by a steel knife) and its smooth, shell-like (conchoidal) fracture pattern. Common in sedimentary basins, riverbeds, and as nodules within limestone outcrops.