sedimentary

Chert (White Chert/Flint)

Chert (Microcrystalline or Cryptocrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: typically white, grey, or tan; Luster: waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: typically white, grey, or tan
Luster: waxy to dull

Identified March 25, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: typically white, grey, or tan; Luster: waxy to dull; Crystal structure: Hexagonal (microscopic); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Formation & geological history

Formed from the accumulation of siliceous remains (like diatoms or radiolaria) or via chemical precipitation in ocean water. It can form as nodules in limestone or as bedded deposits. Geological age varies from Precambrian to Cenozoic.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp conchoidal edges. Currently used in road construction, as an abrasive, and occasionally as a gemstone in the form of jasper or agate.

Geological facts

Chert is so hard it can strike sparks against steel, which is why darker varieties (flint) were used in flintlock firearms. It is chemically identical to quartz but has a different internal microscopic texture.

Field identification & locations

Identify in the field by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in sedimentary basins, riverbeds, and as garden landscaping rock.