sedimentary

Flint / Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale; Color: Varies from white, grey, brown to black; Luster: Waxy to vitreous; Crystal structure: Microcrystalline/cryptocrystalline (quartz); Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.60 - 2.65

Hardness: 7 on the Mohs scale
Color: Varies from white, grey, brown to black
Luster: Waxy to vitreous

Identified July 30, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as nodules in sedimentary rocks such as chalk and limestone through the replacement of calcium carbonate by silica-rich solutions in marine environments over millions of years.

Uses & applications

Historically used for making stone tools, arrowheads, and fire-starting (striking against steel). Occasionally used in decorative items and landscaping.

Geological facts

Flint was one of the most important materials for early humans due to its ability to break with very sharp edges (conchoidal fracture) and its durability.

Field identification & locations

Found worldwide, often weathering out of chalk or limestone cliffs and riverbeds. Identified by its waxy luster, conchoidal fracture, and ability to scratch glass.