sedimentary

Chert (Dark Variety / Flint)

Silicon Dioxide (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 Mohs; Color: Dark brown, black, or deep grey; Luster: Waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 6
Color: Dark brown, black, or deep grey
Luster: Waxy to dull

Identified May 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed from the accumulation of silica-rich organic remains, such as radiolaria or diatoms, in marine environments, or through chemical precipitation in limestone. It typically dates from the Precambrian to the present.

Uses & applications

Historically used for stone tools and starting fires; currently used in construction as road metal, as a gemstone (Jasper/Flint), and as an architectural decorative stone.

Geological facts

Chert is so hard it can scratch steel. When broken, it creates exceptionally sharp edges, which led to its primary role in the development of early human technology for arrowheads and knives.

Field identification & locations

Identify by its waxy texture and conchoidal (shell-like) fracture patterns. It is commonly found as nodules in limestone or chalk beds. Test by scratching a glass plate or striking with steel to produce sparks.