Chert (often called Flint or Jasper)

Physical Properties

Hardness: 7 (Mohs scale), Color: dull yellowish-green to gray with dark inclusions, Luster: waxy to vitreous, Crystal Structure: Cryptocrystalline (microscopic), Cleavage: None (it has conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed through the precipitation of silica-rich fluids within sedimentary rock layers, often replacing limestone or forming as nodules. It commonly originates from the accumulation of microscopic skeletal remains of marine organisms like diatoms and radiolarians.

Uses & Applications

Historically used for making stone tools and starting fires (flint). Currently used as an industrial abrasive, road surfacing material, and occasionally for lapidary work or semi-precious jewelry when vibrantly colored.

Geological Facts

Because of its extreme hardness and conchoidal fracture, chert was the most common material used by prehistoric humans to create sharp-edged tools like arrowheads, scrapers, and knives.

Field Identification & Locations

Identify in the field by its smooth, waxy surface and its tendency to break with sharp, curved 'shell-like' edges (conchoidal fracture). It will scratch glass easily but cannot be scratched by a steel knife. Commonly found in riverbeds and limestone outcrops.

Identified on: 4/24/2026

Mode: Standard