sedimentary

Black Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 (Mohs scale), Color: Dark grey to black with waxy to dull luster, Crystal Structure: Microcrystalline/cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Identified July 5, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: Dark grey to black with waxy to dull luster, Crystal Structure: Microcrystalline/cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed as nodules or layers in sedimentary rocks (like limestone or chalk) through the replacement of calcium carbonate by silica-rich fluids. Common in Cretaceous and Jurassic formations.

Uses & applications

Historically used for stone tools and starting fires; currently used as a grinding media in ball mills and for architectural decoration.

Geological facts

Chert was one of the most important minerals for early humans because its conchoidal fracture creates razor-sharp edges. The location (43.4 N, 40 E) is in the Western Caucasus, a region rich in sedimentary sequences where chert nodules are frequently found within limestone beds.

Field identification & locations

Identify in the field by its smooth, shell-like fracture surfaces and high hardness (it will easily scratch glass). Often has a white or light-colored weathered rind (cortex), as visible on one side of this specimen.