sedimentary

Chert / Flint

Microcrystalline Quartz (SiO2)

Hardness: 7 (Mohs scale), Color: tan, grey, brown with reddish iron staining, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Identified June 23, 2026More sedimentary →

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Physical properties

Hardness: 7 (Mohs scale), Color: tan, grey, brown with reddish iron staining, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific Gravity: 2.65

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation in marine environments, often replacing limestone or dolostone. Dates from various geological eras.

Uses & applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; used today as a hard-wearing road aggregate or in jewelry (as jasper/agate variants).

Geological facts

Chert is so hard it can scratch steel and was famously used in 'flint and steel' fire-starting kits. Its conchoidal fracture makes it the primary material for the ancient art of flintknapping.

Field identification & locations

Identify in the field by its extreme hardness, smooth waxy feel when freshly broken, and the curved 'clamshell' patterns where it has chipped. Commonly found as nodules in limestone beds.