Banded Chert

Physical Properties

Hardness: 7 on Mohs scale; Color: Gray, tan, and dark bands; Luster: Waxy to vitreous; Crystal 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 chemical precipitation in marine environments. Banding represents seasonal or environmental changes during deposition over millions of years.

Uses & Applications

Used historically for stone tools due to sharp edges; currently used for lapidary work, jewelry (tumbled stones), and as an abrasive in some industrial processes.

Geological Facts

Chert was one of the most important materials for early humans to create arrowheads and scrapers. Banded versions are often called 'flint' if found in chalk or marly limestone.

Field Identification & Locations

Identify by its extreme hardness (cannot be scratched by a steel knife) and smooth, shell-like (conchoidal) fractures. Often found in riverbeds or as nodules within limestone outcrops.

Identified on: 4/19/2026

Mode: Standard