Chert (specifically Flint or Jasper variant)

Physical Properties

Hardness: 6.5-7 (Mohs scale), Color: Brownish-red to grey, Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline/cryptocrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.65

Formation & Geological History

Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids. Can be found in nodules within limestone or as bedded layers in marine sequences; ages range from Precambrian to Cenozoic.

Uses & Applications

Used historically for stone tools/weapons (knapping), fire-starting, and currently as road aggregate, in jewelry (as Jasper), and as a gemstone for collectors.

Geological Facts

Chert exhibits conchoidal fracture, allowing it to break into edges sharper than a steel scalpel. It is one of the most durable sedimentary rocks and was a critical resource for prehistoric humans worldwide.

Field Identification & Locations

Identify by its waxy texture, inability to be scratched by steel, and sharp, shell-like (conchoidal) breaking pattern. Common in river beds, limestone outcroppings, and coastal cliffs.

Identified on: 4/16/2026

Mode: Standard