sedimentary

Chert (Flint) with Iron Staining

Microcrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Tan, grey, with reddish-orange iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.75

Hardness: 6
Color: Tan, grey, with reddish-orange iron oxide staining
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 Mohs; Color: Tan, grey, with reddish-orange iron oxide staining; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.6-2.75

Formation & geological history

Formed in marine or freshwater environments via the precipitation of silica. This often occurs when silica-rich fluids replace organic matter or carbonate minerals. The red staining is from secondary iron oxide enrichment.

Uses & applications

Historically used for making stone tools (arrowheads). Today used in road construction, landscaping, and as a component in ceramics.

Geological facts

Chert is so hard it can strike sparks against steel, a property that led to its use in flintlock firearms. The conchoidal fracture creates extremely sharp edges used in prehistoric surgical tools.

Field identification & locations

Identify by its waxy appearance and shell-like (conchoidal) fracture patterns. It cannot be scratched by a steel knife. Common in limestone and chalk deposits globally.