sedimentary

Chert (Iron-stained)

Chert (primarily Microcrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Gray to tan with yellow-brown iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 (Mohs scale)
Color: Gray to tan with yellow-brown iron oxide staining
Luster: Waxy to dull

Identified March 8, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Gray to tan with yellow-brown iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from silica-rich fluids. Often found as nodules in limestone or chalk beds spanning various geological periods from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and arrowheads due to its sharp edges; modern uses include road construction aggregate, landscaping, and occasionally as an abrasive.

Geological facts

Chert is so hard it can create sparks when struck against steel, a property that led to its use in flintlock firearms. The yellowish-orange tint on this specimen is likely due to the oxidation of iron-bearing minerals (limonite or goethite).

Field identification & locations

Identify in the field by its extreme hardness (will scratch glass), waxy luster on fresh surfaces, and characteristic smooth, curved (conchoidal) breaks. Very common in sedimentary basins worldwide.