sedimentary

Flint

SiO2 (Microcrystalline Quartz / Chert)

Hardness: 7 on Mohs scale. Color: Brown, dark grey, black, or yellowish. Luster: Waxy to vitreous. Crystal structure: Trigonal (microcrystalline/cryptocrystalline). Cleavage: None, exhibits conchoidal fracture. Specific gravity: 2.60 to 2.65.

Hardness: 7 on Mohs scale
Color: Brown, dark grey, black, or yellowish
Luster: Waxy to vitreous

Identified July 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms by the chemical replacement of calcium carbonate in limestone or chalk by silica-rich groundwaters, often originating from siliceous skeletal remains of marine organisms such as sponges or diatoms. Associated with Cretaceous chalk deposits.

Uses & applications

Historically used for making stone tools, arrowheads, and striking fire. Today used for decorative aggregate, building stone, ball mills for grinding, and occasional lapidary purposes.

Geological facts

Flint was one of the earliest materials manipulated by early humans to create cutting tools and weapons due to its sharp conchoidal fracture edges when struck.

Field identification & locations

Easily identified by its conchoidal (shell-like) fracture, waxy luster, and high hardness that easily scratches glass. Commonly found as nodules within chalk or limestone formations worldwide.