sedimentary

Chert (Flint)

Microcrystalline Quartz (SiO2)

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

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

Identified July 1, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed by the accumulation of siliceous remains of microscopic organisms like diatoms or radiolarians, or through chemical precipitation of silica from groundwater in limestone or chalk beds.

Uses & applications

Historically used for making stone tools (arrowheads, knives) due to its sharp edges; used today as road surfacing material and for fire-starting in survival kits.

Geological facts

Chert has been used by humans for over 2 million years. When struck against steel, it produces sparks used to ignite gunpowder or tinder.

Field identification & locations

Identify by its characteristic shell-like (conchoidal) fracture pattern and its ability to scratch glass. Commonly found in nodular or bedded form within limestone outcrops.