sedimentary

Chert (Flint)

Chert (Microcrystalline or cryptocrystalline Quartz, SiO2)

AI-generated identification · may be incorrect

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

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

Identified June 21, 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 (microscopic crystals); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Forms primarily through the accumulation of silica-rich organic debris (such as radiolaria or diatoms) or by chemical precipitation in sedimentary environments like deep sea floors or limestone beds.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as a decorative stone, in road construction, and for fire-starting strikers.

Geological facts

Flint is a variety of chert that occurs in chalk or marly limestone. It was one of the most important minerals for early human survival, used globally to create tools during the Stone Age.

Field identification & locations

Identified by its extremely hard surface (it can scratch glass), waxy feel, and sharp shell-like (conchoidal) fractures. Found in riverbeds, limestone outcrops, and coastal areas.