sedimentary

Flint / Chert

Microcrystalline quartz (SiO2)

Hardness: 7 on Mohs scale. Color: Tan, brown, gray, or yellowish-white. Luster: Waxy to vitreous. Crystal structure: Cryptocrystalline / trigonal (microscopic quartz fibers). Cleavage: None (exhibits prominent conchoidal fracture). Specific gravity: 2.60 to 2.65.

Hardness: 7 on Mohs scale
Color: Tan, brown, gray, or yellowish-white
Luster: Waxy to vitreous

Identified August 3, 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 limestone or chalk formations over millions of years during the Cretaceous period.

Uses & applications

Historically used for making stone tools, arrowheads, and blades due to its sharp conchoidal fracture. Also used for fire-starting with steel, and in modern decorative or building aggregates.

Geological facts

Flint and chert are chemically identical, both being forms of microcrystalline quartz. Flint traditionally refers to varieties found in chalk formations, while chert is found in limestone.

Field identification & locations

Easily identified by its characteristic smooth, curved conchoidal fracture surfaces, waxy luster, and high hardness (scratches glass). Commonly found in chalk and limestone deposits worldwide.