sedimentary

Chert (or Flint)

Microcrystalline Quartz (SiO2)

Hardness: 7 Mohs scale; Color: Grey, brown, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Hardness: 7 Mohs scale
Color: Grey, brown, or tan
Luster: Waxy to dull

Identified June 3, 2026More sedimentary →

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Physical properties

Hardness: 7 Mohs scale; Color: Grey, brown, or tan; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7

Formation & geological history

Forms primarily through the replacement of limestone by silica-rich fluids or the accumulation of siliceous remains such as diatoms or radiolarians in marine environments. Can occur as nodules or bedded deposits.

Uses & applications

Historically used for stone tools and weapons (arrowheads); currently used as a raw material for construction aggregate, in metallurgy, and as a starting material for silicon.

Geological facts

Chert has been used by humans for millions of years because it breaks into sharp edges through conchoidal fracturing. The variety known as 'flint' was essential for starting fires and in early firearms.

Field identification & locations

Identify by its smooth, waxy texture and sharp, shell-like (conchoidal) breakage patterns. It is very hard and will scratch glass. Commonly found in limestone formations or as river pebbles.