sedimentary

Flint (or Chert)

Silicon dioxide (Microcrystalline Quartz, $SiO_2$)

Hardness: 7 on the Mohs scale. Color: Dark brown, black, grey, or light tan. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline or microcrystalline quartz (chalcedony). Cleavage: Conchoidal fracture, meaning it breaks with smooth, curved surfaces resembling the inside of a curved shell.

Hardness: 7 on the Mohs scale
Color: Dark brown, black, grey, or light tan
Luster: Waxy to vitreous

Identified August 1, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the replacement of calcium carbonate by silica-rich solutions in sedimentary environments, typically within chalk or limestone formations over millions of years.

Uses & applications

Historically used by early humans to manufacture stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used historically to strike against steel to create sparks for starting fires.

Geological facts

Flint and chert are chemically identical, though archaeologists and geologists often reserve the term 'flint' for the darker varieties found specifically in chalk deposits.

Field identification & locations

Easily identified by its distinctive waxy luster, hardness (scratches glass), and razor-sharp conchoidal fracture edges. Commonly found as nodules or layers within limestone and chalk cliffs worldwide.

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