Chert (often called Flint in this context)

Physical Properties

Hardness: 7 (Mohs scale). Color: White, tan, brown, or red/orange (iron staining). Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic quartz). Cleavage: None (conchoidal fracture). Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments, often as nodules within limestone or chalk beds. Most widespread during the Paleozoic and Mesozoic eras.

Uses & Applications

Historically used for stone tools and arrowheads. Currently used in road construction as aggregate, as a component in ceramics, and occasionally for lapidary work or fire-starting kits.

Geological Facts

Chert breaks with a conchoidal (shell-like) fracture, creating sharp edges that were vital to prehistoric human technology. It can produce sparks when struck against steel, a property caused by small particles of metal being shorn off and oxidizing rapidly.

Field Identification & Locations

Identify by its hardness (it will scratch glass and steel) and its distinctive waxy texture and curved fracture surfaces. Commonly found in stream beds or weathering out of limestone cliffs.

Identified on: 5/20/2026

Mode: Standard