Chert (Jasper/Flint variety)

Physical Properties

Hardness: 6.5-7 (Mohs); Color: tan, brown, reddish-orange; Luster: waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: none (conchoidal fracture); Specific gravity: 2.65.

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments, often replacing original limestone or chalk during diagenesis.

Uses & Applications

Historically used for making stone tools (arrowheads); currently used in road construction, as an abrasive, and occasionally for lapidary work if highly colored.

Geological Facts

Chert is so hard it can scratch steel. It is one of the most common materials used by prehistoric humans for tool-making because it breaks with sharp edges like glass.

Field Identification & Locations

Identify by its 'flint-like' waxy texture, smooth conchoidal (shell-like) fracture surfaces, and high hardness. Commonly found in riverbeds, glacial tills, and as nodules in limestone outcrops.

Identified on: 4/25/2026

Mode: Standard