sedimentary

Chert (Flint Nodules)

Sedimentary cryptocrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 (Mohs scale); Color: Dark brown, black, or grey; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 (Mohs scale)
Color: Dark brown, black, or grey
Luster: Waxy to vitreous

Identified July 17, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale); Color: Dark brown, black, or grey; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through a chemical or biological process where silica precipitates out of groundwater or is concentrated from the remains of silica-shelled organisms in limestone or chalk beds. Often Cretaceous or Jurassic in age.

Uses & applications

Historically used for making stone tools (arrowheads, knives) due to its sharp conchoidal fracture. Used modernly as a decorative landscape stone and in some road construction.

Geological facts

Flint was one of the most important minerals for early humans, used both for tools and as a fire-starter because it creates sparks when struck against steel. The dark color often comes from trapped organic matter.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) breaking pattern and its ability to scratch glass. It often features a white outer 'cortex' or weathered layer when found in chalk deposits.