sedimentary

Flint

SiO2 (Microcrystalline Quartz / Chert)

AI-generated identification · may be incorrect

Hardness of 7 on the Mohs scale; dark gray to black or brown color with lighter quartz or chalky veins; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture with very sharp edges; specific gravity of around 2.60.

Identified July 29, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the chemical replacement of calcium carbonate in limestone or chalk by silica-rich solutions derived from sponge spicules or other silica-secreting organisms, typically during the Cretaceous period.

Uses & applications

Historically used for making stone tools, arrowheads, and striking fire with steel. Today used for decorative landscaping, abrasives, and sometimes in specialized ball mills.

Geological facts

Flint and chert are essentially the same material, though 'flint' typically refers to the dark nodules found specifically in chalk deposits. Due to its conchoidal fracture, it was one of the most prized materials for prehistoric toolmaking.

Field identification & locations

Found worldwide within chalk or limestone formations. Identified easily by its dark, dull-to-waxy appearance, conchoidal fracture surfaces, and high hardness which can easily scratch glass.