sedimentary

Flint or Chert

Microcrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: typically dark gray, black, or brown with tan weathered rind; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none, shows distinctive conchoidal fracture.

Hardness: 7 on Mohs scale
Color: typically dark gray, black, or brown with tan weathered rind
Luster: waxy to dull

Identified June 23, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed as nodules or masses in sedimentary rocks like chalk and limestone; precipitates from silica-rich fluids through chemical replacement during diagenesis.

Uses & applications

Historically used for stone tools and starting fires; currently used as a grinding medium in ball mills, in road construction, and for decorative lapidary work.

Geological facts

Flint was one of the first materials used by early humans to create sharp cutting tools and weapons due to its predictable fracturing pattern. It can create sparks when struck against steel.

Field identification & locations

Identify by its glass-like conchoidal fractures, sharp edges when broken, and extreme hardness (will scratch glass). Commonly found in areas with chalk or limestone deposits.