sedimentary

Chert (Iron-stained)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Grayish-white with orange-brown iron staining (limonite/hematite); Luster: Waxy to dull; Crystal structure: Microcrystalline/cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Luster: Waxy to dull

Identified April 8, 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 from silica-saturated fluids in limestone or dolomite beds. This process typically occurs in marine environments over millions of years.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges when fractured. Modern uses include road surfacing, glass manufacturing (if high purity), and decorative landscaping stones.

Geological facts

Chert is so hard that it can strike sparks against steel, which is why certain types like flint were essential for starting fires and early firearms. The orange staining is caused by secondary oxidation of iron-bearing minerals.

Field identification & locations

Identify in the field by its hardness (will scratch glass), smooth conchoidal (shell-like) fracture edges, and waxy texture. Commonly found in regions with prehistoric limestone outcroppings or as alluvial gravel in riverbeds.

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