sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Grey, tan, brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 Mohs scale
Color: Grey, tan, brown
Luster: Waxy to dull

Identified July 9, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Grey, tan, brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Formed primarily in marine environments where silica-rich fluids replace carbonate minerals or accumulate from radiolarian/diatom remains. Can occur as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used in road construction, as a strike-a-light for starting fires, and for jewelry in its colorful forms.

Geological facts

Chert has been used by humans for over 2 million years. When struck against steel, it produces sparks due to its hardness and friction, making it vital for early firearms like flintlocks.

Field identification & locations

Identify by its conchoidal (shell-like) fracture patterns and ability to scratch glass. Found globally in sedimentary basins, riverbeds, and as nodules in limestone outcrops.