sedimentary

Black Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Black with white limestone/calcite cortex; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Black with white limestone/calcite cortex
Luster: Waxy to dull

Identified July 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed by the accumulation of siliceous remains of marine organisms (like diatoms or radiolarians) or chemical precipitation of silica within limestone or chalk beds. Likely dating to the Cretaceous or Jurassic periods, which are prominent in the Caucasus mountain region near the reported coordinates.

Uses & applications

Historically used for stone tools and starting fires; currently used as a decorative stone, in construction aggregate, and by flintknappers.

Geological facts

This specimen shows classic conchoidal (shell-like) fracturing, which allows it to create edges sharper than a steel scalpel. The white portion is likely the 'cortex,' the outer weathered or limestone-rich layer where the chert nodule formed.

Field identification & locations

Identify in the field by its hardness (will scratch glass), waxy feel, and sharp, curved edges when broken. The location in the Caucasus (43.4 N, 40.0 E) is consistent with the region's rich sedimentary sequences where chert nodules are frequently found.