sedimentary

Chert (Iron-stained)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale); Color: Rusty orange/brown due to iron oxide staining; Luster: Waxy to dull; Structure: Non-crystalline visible grains; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Rusty orange/brown due to iron oxide staining
Luster: Waxy to dull

Identified March 20, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds. Geological age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and starting fires (flint). Modern uses include road aggregate, decorative landscaping, and occasionally as a gemstone when color patterns are unique (Jasper).

Geological facts

Chert is so hard that it can scratch steel. The reddish hue In this specimen is likely due to 'limonite' or 'hematite' staining, which occurs when iron-rich water permeates the rock over time.

Field identification & locations

Identify by its 'conchoidal' (shell-like) fracture patterns and ability to scratch glass. It is commonly found in gravel pits, riverbeds, and as nodules in sedimentary outcrops across North America and Europe.

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