Chert (Jasper variation)

Physical Properties

Hardness: 6.5–7 on Mohs scale; Color: Tan, brown, and yellowish-brown with dark speckles; Luster: Waxy to dull; Crystal structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.6–2.7

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from silica-rich fluids within other sedimentary rocks like limestone. Often found in nodules or bedded layers across various geological ages.

Uses & Applications

Commonly used in prehistoric times for tool-making (arrowheads, scrapers) due to its sharp conchoidal fracture. Today it is used in road construction as aggregate, in jewelry as semi-precious gemstones (Jasper), and as flint for fire-starting.

Geological Facts

Chert is so hard it can scratch steel and was used for centuries in flintlock firearms. This specific piece shows river-worn smooth surfaces combined with sharp angular breaks typical of silica rocks.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a knife), waxy appearance, and the way it breaks into curved, shell-like (conchoidal) shapes. Commonly found in riverbeds, limestone outcrops, and coastal areas.

Identified on: 4/27/2026

Mode: Standard