sedimentary

Chert (Flint / Chalcedony pebble)

Silicon Dioxide (SiO2)

Hardness: 6.5 - 7 on the Mohs scale. Color: Brownish-gray, translucent to opaque. Luster: Waxy to vitreous or dull. Cleavage: None (shows characteristic conchoidal fracture). Microcrystalline structure.

Hardness: 6
Color: Brownish-gray, translucent to opaque
Luster: Waxy to vitreous or dull

Identified July 27, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation and chemical precipitation of silica-rich biogenic sediment (like radiolarian or sponge spicules) or chemical replacement of carbonates in sedimentary marine environments, often tumbled into smooth pebbles by water action.

Uses & applications

Historically used for stone tools, arrowheads, and spark-striking fire starters due to its sharpness when fractured and high hardness. Currently used in jewelry, landscaping, and lapidary tumbling.

Geological facts

Chert and flint were among the very first materials used by early humans in the Stone Age to manufacture sharp tools. It produces a sharp edge that can be sharper than a modern surgical scalpel.

Field identification & locations

Identify in the field by its hardness (scratches glass easily), waxy luster, and distinctive curved (conchoidal) shell-like fractures along chipped edges. Very common along gravel beds, riverbanks, and beaches worldwide.

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