sedimentary

Chert (Iron-stained)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: tan, white, brown, and reddish-pink due to iron oxidation, Luster: waxy to dull, Crystal structure: microcrystalline/cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.6-2.7

Identified June 9, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation from groundwater within sedimentary layers. This specimen likely originates from a limestone or dolostone formation where silica replaced original carbonate minerals.

Uses & applications

Used historically for stone tools and weapons due to its sharp edges when fractured. Modern uses include construction aggregate, road base, and occasionally lapidary work for jewelry if colorful enough.

Geological facts

Chert is so durable that it often remains as 'float' in soil long after the surrounding limestone has weathered away. The reddish veins in this piece are 'limonite' or 'hematite' staining caused by the oxidation of iron minerals.

Field identification & locations

Identify in the field by its high hardness (it will scratch glass and steel), its smooth waxy feel on fresh breaks, and its characteristic curved (conchoidal) fracture pattern. Found globally in sedimentary basins.