sedimentary

Chert / Flint

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale. Color: Highly variable, typically grey, black, or brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic silica crystals). Cleavage: None (exhibits conchoidal/shell-like fracture). Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Highly variable, typically grey, black, or brown
Luster: Waxy to dull

Identified March 18, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. It can form as nodules in limestone or chalk beds. Geological age ranges from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools and weapons (arrowheads, scrapers) due to its sharp edges. Currently used in road construction, as an abrasive, and sometimes in jewelry (as jasper or flint).

Geological facts

Because of its ability to produce sparks when struck against steel, it was the primary ignition source for flintlock firearms for centuries. It breaks into glass-sharp edges that are still used in some specialized surgical scalpels.

Field identification & locations

Identify in the field by its very smooth, glass-like fracture surfaces and extreme hardness (it will scratch glass). It is commonly found in riverbeds, glacial till, and embedded in limestone cliffs. It is a favorite for lapidary tumbling.