sedimentary

Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on the Mohs scale. Color: Varies from white, grey, brown, to dark brown or black. Luster: Vitreous to dull. Crystal structure: Cryptocrystalline or microcrystalline quartz (chalcedony). Cleavage: None, exhibits prominent conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on the Mohs scale
Color: Varies from white, grey, brown, to dark brown or black
Luster: Vitreous to dull

Identified August 5, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical precipitation of silica from aqueous solutions, often replacing carbonate rocks like limestone during diagenesis, or from the accumulation of siliceous skeletal remains of marine organisms such as radiolarians and diatoms.

Uses & applications

Historically used extensively by ancient humans for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used historically for striking fire.

Geological facts

Chert is remarkably durable and resistant to weathering, which is why ancient stone artifacts made from chert survive exceptionally well in the archaeological record.

Field identification & locations

Can be identified in the field by its distinct conchoidal fracture, sharp edges when broken, waxy luster, and high hardness that easily scratches glass.