sedimentary

Flint (chert), likely chalcedony-rich variety

Microcrystalline quartz, SiO₂; flint is a dense cryptocrystalline form of chert

AI-generated identification · may be incorrect

Typically Mohs 6.5–7, waxy to dull luster, conchoidal fracture, and translucent gray-brown to amber coloration; the specimen shows weathered iron-oxide staining and possibly thin chalcedony zones. Quartz is trigonal, though crystals are generally microscopic.

Identified September 11, 2026More sedimentary →

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Physical properties

Formation & geological history

Forms mainly by silica replacement or concentration within marine limestone and chalk, commonly during the Cretaceous or younger sedimentary history. Iron-bearing fluids can produce orange, red, and brown colors.

Uses & applications

Used historically for stone tools and fire-starting, and today as a collectible, lapidary material, aggregate, and decorative stone; translucent material may be polished.

Geological facts

Its sharp conchoidal edges were crucial to prehistoric toolmaking. Flint and chert are closely related terms, with “flint” often referring to dark chert from chalk environments.

Field identification & locations

Identify by testing for conchoidal fracture, glassy/waxy surfaces, and inability to scratch it with a steel knife; it should scratch glass. Common in chalk and limestone regions worldwide, including England, France, Texas, and the Midwest U.S.