sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: Brown, tan, and grey, Luster: Waxy or dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Identified June 7, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Brown, tan, and grey, Luster: Waxy or dull, Crystal structure: Cryptocrystalline, Cleavage: None (conchoidal fracture)

Formation & geological history

Formed as nodules or beds in sedimentary rocks through the precipitation of silica from aqueous solutions or the accumulation of silica-rich organic remains like sponges or diatoms.

Uses & applications

Historically used for stone tools and weapons (flintknapping); currently used in road construction, abrasive sand, and occasionally in lapidary work.

Geological facts

Chert is known for its incredible durability and its ability to break into razor-sharp edges, a property that allowed early humans to develop primitive technology.

Field identification & locations

Identified in the field by its hardness (scratches glass), waxy luster on fresh surfaces, and characteristic smooth, curved conchoidal fractures. Commonly found in limestone and chalk deposits.