sedimentary

Chert (Iron-stained)

Chert (SiO2)

Hardness: 7 (Mohs scale); Color: tan, brown, and yellow due to iron oxide staining; Luster: waxy to dull; Crystal structure: microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: tan, brown, and yellow due to iron oxide staining
Luster: waxy to dull

Identified April 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the precipitation of silica from seawater or the accumulation of siliceous skeletal remains (like diatoms or radiolarians) that undergo diagenesis. This specimen appears weathered and stained by groundwater minerals.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges when broken. Today used as road aggregate, in landscaping, and as a polishing material for lapidary work.

Geological facts

Chert is so hard it can scratch steel and even spark when struck against iron. This specific variety is often colloquially called 'flint' if it is dark and 'Jasper' if it is colorful and opaque.

Field identification & locations

Identify in the field by its conchoidal (shell-like) fracture pattern and its inability to be scratched by a steel knife. It is extremely common in areas with limestone or dolomite deposits.