Chert (specifically Jasper or Flint type)

Physical Properties

Hardness: 7 (Mohs), Color: Tan to reddish-orange, Luster: Waxy to vitreous, Crystal Structure: Trigonal (microcrystalline), Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed primarily through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation from groundwater within sedimentary layers. This process can occur over millions of years, often in limestone or chalk beds.

Uses & Applications

Historically used for making stone tools (arrowheads, scrapers) due to its sharp conchoidal fracture. Today used as an abrasive, in landscaping, and as a semi-precious gemstone in jewelry when it displays attractive colors (Jasper).

Geological Facts

Chert has been used by humans for hundreds of thousands of years to create fire (by striking against steel) and edges sharper than a surgical scalpel. It is one of the most durable sedimentary rocks.

Field Identification & Locations

Identify by its smooth, waxy feel and the way it breaks into curved, shell-like flakes (conchoidal fracture). It cannot be scratched by a steel knife. Frequently found in stream beds or eroding out of limestone cliffs.

Identified on: 5/10/2026

Mode: Standard