sedimentary

Chert (Flint)

Silicon Dioxide (SiO2)

Hardness: 7 on Mohs scale; Color: brown, tan, gray, or yellow; Luster: vitreous to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6

Hardness: 7 on Mohs scale
Color: brown, tan, gray, or yellow
Luster: vitreous to waxy

Identified March 14, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: brown, tan, gray, or yellow; Luster: vitreous to waxy; Structure: Microcrystalline/cryptocrystalline; Cleavage: none (conchoidal fracture); Specific Gravity: 2.6

Formation & geological history

Formed by the precipitation of silica from seawater or groundwater. Commonly found in limestone or chalk beds as nodules or layers. Known for forming over various geological ages, notably in Paleozoic and Mesozoic sedimentary basins.

Uses & applications

Used historically for stone tools and weapons due to its sharpness when fractured; currently used in construction as road base, as an abrasive, and sometimes in jewelry as tumbled stones.

Geological facts

Also known as the stone of fire because it creates sparks when struck against steel. Flint is technically a dark-colored variety of chert. It has been used by humans for over 2 million years.

Field identification & locations

Identify by its 'conchoidal' (shell-like) fracture edges that are extremely sharp. Common in riverbeds and limestone outcrops globally. High value for flintknapping hobbyists.