sedimentary

Chert (White Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: white to off-white with tan inclusions; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: white to off-white with tan inclusions
Luster: waxy to dull

Identified June 28, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: white to off-white with tan inclusions; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Forms through the precipitation of silica from groundwater or the accumulation of siliceous remains of marine organisms (like diatoms) in limestone or chalk beds. It can date from various geological periods, often associated with Cretaceous chalk.

Uses & applications

Historically used for stone tools and starting fires; modernly used as a decorative stone, in construction aggregate, and occasionally in jewelry as a cabochon.

Geological facts

Chert breaks with a conchoidal fracture, creating sharp edges that were essential for prehistoric arrowheads and scrapers. When struck against steel, it creates sparks, hence the name 'Flint'.

Field identification & locations

Identify in the field by its hardness (it will scratch glass), its waxy feel, and the distinctive curved, shell-like (conchoidal) breaks. Often found as nodules within limestone or chalk outcrops.