sedimentary

Chert (Flint Nodule)

Microcrystalline and Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Grey, tan, black, and brown with a waxy to dull luster; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Hardness: 7 on Mohs scale
Color: Grey, tan, black, and brown with a waxy to dull luster

Identified July 18, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey, tan, black, and brown with a waxy to dull luster; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds. This occurs as a replacement process where silica fills voids or replaces carbonate material, typically during the diagenesis of sedimentary layers.

Uses & applications

Historically used for stone tools (arrowheads, knives) due to its sharp conchoidal fracture. Today used as a source of silica, in construction aggregates, and as decorative river rock or lapidary material.

Geological facts

Flint was one of the most important minerals for early human survival, used both for tools and to spark fires. Many large nodules found today in riverbeds or coastal areas are millions of years old, originating from Cretaceous-aged chalk deposits.

Field identification & locations

Identify in the field by its smooth, waxy surface when broken, and its ability to scratch glass. Often found as rounded nodules in riverbeds, fields, or coastal cliffs. Look for the characteristic 'oyster-shell' shaped fracture marks.