sedimentary

Chert (Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 6.5–7 on the Mohs scale. Color: ranges from grey, black, brown, to tan. Luster: Vitreous to waxy. Crystal Structure: Trigonal (microcrystalline). Cleavage: None (exhibits conchoidal fracture). Specific Gravity: 2.65.

Hardness: 6
Color: ranges from grey, black, brown, to tan
Luster: Vitreous to waxy

Identified March 21, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (such as diatoms or radiolaria) or through the chemical precipitation of silica in groundwater. Often found as nodules in limestone or chalk beds, or as bedded deposits.

Uses & applications

Historically used for making stone tools (arrowheads, knives) due to its sharp conchoidal fracture. Modern uses include road surfacing, construction aggregate, and as a component in ceramics.

Geological facts

Dark-colored chert is often specifically called 'flint'. It was one of the most important minerals for early human survival, used both for weaponry and for generating sparks to start fires.

Field identification & locations

Identify in the field by its smooth, waxy feel and characteristic curved (conchoidal) breakage patterns that produce razor-sharp edges. Commonly found in riverbeds, glacial till, or eroding out of limestone cliffs.

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