sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7 on Mohs scale
Color: Brown, tan, or grey
Luster: Waxy to dull

Identified May 24, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Brown, tan, or grey; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed via the accumulation of siliceous remains of organisms (like diatoms or radiolaria) or through chemical precipitation of silica-rich fluids in sedimentary rock layers such as limestone.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction aggregate and occasionally as a gemstone in tumbled forms.

Geological facts

Flint was the primary material for the Stone Age technology due to its ability to split into thin, razor-sharp edges. It produces sparks when struck against steel.

Field identification & locations

Identify by its smooth, waxy surface and its characteristic 'shell-like' conchoidal fracture patterns. Found globally in nodules within chalk or limestone beds.