sedimentary

Chert

Microcrystalline quartz (SiO2)

Hardness: 7 on the Mohs scale. Color varies widely from white, grey, brown, to black. Luster ranges from waxy to vitreous. Crystal structure is cryptocrystalline (microscopic quartz crystals). Fracture is conchoidal.

Hardness: 7 on the Mohs scale

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 originating from the accumulation of silica-rich skeletal remains of microscopic organisms like radiolarians or diatoms in marine environments. Geological age varies from Precambrian to Cenozoic.

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 that is dark-colored or black is commonly referred to as flint. It is extremely durable and weather-resistant, which is why ancient tools made from it survive exceptionally well in the archaeological record.

Field identification & locations

Can be identified in the field by its hard, dense nature, waxy luster, and distinctive conchoidal fracture which creates extremely sharp edges. Commonly found in limestone and chalk formations worldwide.