sedimentary

Chert (specifically Silex or Flint)

Microcrystalline Quartz (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Variegated brown, yellow, and grey; Luster: Waxy to dull; Crystal structure: Cryptocrystalline/Triagonal; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Hardness: 6
Color: Variegated brown, yellow, and grey
Luster: Waxy to dull

Identified June 14, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed primarily through the chemical precipitation of silica or the replacement of limestone by silica-rich fluids. This specimen, found in Central Europe (Czech Republic), is likely associated with Cretaceous or Jurassic sedimentary deposits common to the Bohemian Massif's sedimentary cover.

Uses & applications

Historically used for making stone tools (arrowheads, scrapers) and as strike-a-lights. Today used as an abrasive, in construction aggregate, and as a semi-precious lapidary material.

Geological facts

Flint was the first 'high-tech' material of prehistoric humans due to its ability to produce razor-sharp edges. The location (49.7°N, 15.1°E) is near the Kutná Hora and Bohemian-Moravian Highlands, areas known for diverse mineralogy including chert varieties.

Field identification & locations

Identify in the field by its sharp, glass-like (conchoidal) fractures and its inability to be scratched by a steel knife. It often features a white or chalky outer 'rind' (cortex).

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