Chert (Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: ranges from grey-tan to brownish; Luster: waxy to dull; Crystal Structure: Cryptocrystalline (microscopic quartz); Cleavage: none, exhibits conchoidal fracture.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine or groundwater environments. Often found as nodules in limestone or chalk beds.

Uses & Applications

Historically used for making sharp tools like arrowheads and flintlock ignition systems. Today used as a decorative stone, in road construction, and for aquarium or garden landscaping.

Geological Facts

Chert is so hard it can scratch steel and produce sparks when struck against iron, which is why it was the primary material for flintlock firearms.

Field Identification & Locations

Identify by its 'waxy' texture and smooth, shell-like (conchoidal) breakage patterns. Often found in riverbeds or eroded out of sedimentary cliffs. It is a common 'river rock' due to its extreme durability.

Identified on: 4/16/2026

Mode: Standard