Chert (Iron-stained)

Physical Properties

Hardness: 7 (Mohs scale), Color: Brown to tan with iron staining, Luster: Waxy to dull, Crystal structure: Microcrystalline/Cryptocrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed from the accumulation of siliceous remains of microscopic organisms (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. This specimen shows significant iron oxide staining from exposure to mineral-rich fluids.

Uses & Applications

Historically used for stone tools (arrowheads and scrapers) due to its sharp edges; currently used for road ballast, construction aggregate, and as a collector's specimen.

Geological Facts

Chert is so hard it can scratch steel. It was one of the most important minerals for early humans because of its ability to fracture into extremely sharp, predictable edges.

Field Identification & Locations

Identify in the field by its conchoidal (shell-like) fracture, extreme hardness (cannot be scratched by a knife), and smooth, waxy texture. It is commonly found in limestone or dolomite formations.

Identified on: 4/14/2026

Mode: Standard