sedimentary

Chert (Flint)

Chert (SiO2)

AI-generated identification · may be incorrect

Hardness: 6.5-7 (Mohs); Color: Grey, black, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Hardness: 6
Color: Grey, black, or tan
Luster: Waxy to dull

Identified May 9, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs); Color: Grey, black, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific gravity: 2.65

Formation & geological history

Formed as nodules or layered deposits in limestone or chalk through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from groundwater.

Uses & applications

Historically used for stone tools (arrowheads, knives) and strike-a-lights. Currently used in construction aggregate and as a collector's specimen.

Geological facts

Chert is so hard it can scratch steel and was the primary material for the 'Stone Age' technology. When struck against steel, it produces sparks used for starting fires.

Field identification & locations

Identify by its extremely smooth, shell-like (conchoidal) fracture and waxy texture. Commonly found in riverbeds, glacial till, or embedded within limestone outcrops.