sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: Grey, black, or tan with a waxy or dull luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

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

Identified May 29, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Grey, black, or tan with a waxy or dull luster; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the replacement of limestone by silica-rich groundwater. Often found in nodules within limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons (arrowheads, knives); used today in construction aggregate, road base, and as a component in glass manufacturing.

Geological facts

Chert was one of the most important minerals for early humans due to its ability to create sharp edges when struck. High-quality black chert is often specifically called 'Flint'.

Field identification & locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass easily. Commonly found in riverbeds or as nodules protruding from limestone outcrops.