Chert (specifically Zebra Chert/Flint)

Physical Properties

Hardness: 7 (Mohs scale), Color: Banded gray and white, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline (Hexagonal), Cleavage: None (Conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich microfossils or chemical precipitation in marine environments. The banding often results from fluctuating chemical conditions or rhythmic sediment deposition. It can range from Precambrian to Cenozoic in age.

Uses & Applications

Historically used for stone tools (knapping) due to its sharp edges. Modern uses include jewelry (cabochons), as an industrial abrasive, and as a landscaping stone.

Geological Facts

Because of its high silica content and density, chert was one of the primary materials used by prehistoric humans to create arrowheads, scrapers, and blades. It sparks when struck against steel, which made it essential for flintlock firearms.

Field Identification & Locations

Identify by its waxy texture and characteristic shell-like (conchoidal) fractures. It is harder than steel and will easily scratch glass. Found globally in limestone formations and as nodules in stream beds.

Identified on: 4/23/2026

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