Chert (White Chert)

Physical Properties

Hardness: 7 on Mohs scale; Color: Off-white to beige; Luster: Waxy to dull; Structure: Cryptocrystalline; Cleavage: None (Conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

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

Uses & Applications

Abrasives, construction aggregate, and historically used for stone tools/weaponry due to its sharp edges; used today as landscaping stones or for lapidary tumbling.

Geological Facts

Chert is so hard it can create sparks when struck against steel. This specific specimen shows signs of water erosion and possible thermal fracturing or 'crazing' on the surface.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by steel) and smooth, shell-like (conchoidal) fractures. Often found in gravel beds or eroding out of limestone cliffs.

Identified on: 4/20/2026

Mode: Standard