sedimentary

Chert / Flint

Silicon Dioxide (Microcrystalline Quartz, $SiO_2$)

Hardness: 7 on the Mohs scale. Color: Varies from gray, white, brown, to black. Luster: Waxy to vitreous. Crystal Structure: Microcrystalline or cryptocrystalline (chalcedony). Cleavage: None, exhibits conchoidal fracture.

Hardness: 7 on the Mohs scale
Color: Varies from gray, white, brown, to black
Luster: Waxy to vitreous

Identified August 3, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by the replacement of calcium carbonate by silica in limestone or chalk during diagenesis, or through the accumulation of siliceous skeletal remains of marine organisms such as diatoms and radiolarians.

Uses & applications

Historically used for making stone tools, arrowheads, and striking fire. Also used in abrasives, road construction, and occasionally decorative or lapidary purposes.

Geological facts

Chert and flint are chemically identical forms of microcrystalline quartz; the term 'flint' is often used specifically for darker varieties found in chalk formations.

Field identification & locations

Easily identified by its distinctive conchoidal (shell-like) fracture, sharp edges when broken, and high hardness that scratches glass. Commonly found within limestone or chalk beds worldwide.

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