sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale; Color: White, grey, yellowish, or brown; Luster: Vitreous to waxy or dull; Crystal structure: Microcrystalline/cryptocrystalline quartz; Cleavage: None, exhibits conchoidal fracture; Specific gravity: 2.60 to 2.65

Hardness: 7 on the Mohs scale
Color: White, grey, yellowish, or brown
Luster: Vitreous to waxy or dull

Identified August 4, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of silica from aqueous solutions, often replacing limestone or accumulating from the microscopic skeletal remains of silica-secreting organisms like radiolarians and diatoms over millions of years.

Uses & applications

Historically used by ancient humans for making stone tools such as arrowheads and spear points due to its sharp conchoidal fracture. Also used historically for striking fire.

Geological facts

Chert is extremely durable and weather-resistant, which is why ancient stone tools made from it survive exceptionally well in the archaeological record. Varieties of chert include flint and jasper.

Field identification & locations

Can be identified in the field by its high hardness (scratches glass easily), smooth or waxy luster, and characteristic conchoidal fracture resembling broken glass. Commonly found within limestone and chalk formations worldwide.