sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, white, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Fracture: Conchoidal (shell-like curves); Specific gravity: 2.6-2.7

Hardness: 7 on Mohs scale
Color: Gray, tan, white, or brown
Luster: Waxy to dull

Identified July 1, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, white, or brown; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Fracture: Conchoidal (shell-like curves); Specific gravity: 2.6-2.7

Formation & geological history

Formed primarily through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds. Most specimens can range from Cambrian to recent geological ages.

Uses & applications

Historically used for stone tools and weapons due to sharp edges when fractured. Currently used in road construction, as grinding media in ball mills, and by hobbyists for flint knapping or fire-starting.

Geological facts

Chert is so hard it can scratch glass and produces sparks when struck against steel. It was the primary material used by prehistoric humans to create arrowheads and scrapers.

Field identification & locations

Identify in the field by its sharp, curved fracture edges and its inability to be scratched by a steel knife. Commonly found as nodules or layers within sedimentary limestone outcrops.