sedimentary

Chert

Microcrystalline quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on the Mohs scale. Color: Gray, brown, black, white, or green. Luster: Waxy to vitreous. Crystal structure: Microcrystalline/cryptocrystalline. Conchoidal fracture, no cleavage.

Hardness: 7 on the Mohs scale
Color: Gray, brown, black, white, or green
Luster: Waxy to vitreous

Identified July 29, 2026More sedimentary →

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Physical properties

Hardness: 7 on the Mohs scale. Color: Gray, brown, black, white, or green. Luster: Waxy to vitreous. Crystal structure: Microcrystalline/cryptocrystalline. Conchoidal fracture, no cleavage.

Formation & geological history

Formed via chemical precipitation from silica-rich solutions in marine environments or through the replacement of limestone or chalk by silica during diagenesis.

Uses & applications

Historically used for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used in construction aggregate and historically for starting fires when struck against steel.

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 include flint, jasper, and chalcedony.

Field identification & locations

Identify by its hardness (scratches glass), waxy luster, and characteristically sharp conchoidal fracture. Commonly found in limestone and chalk formations worldwide.