Chert (specifically Red Chert or Jasper)

Physical Properties

Hardness: 6.5-7 Mohs; Color: reddish-brown due to iron oxide; Luster: vitreous to waxy; Structure: cryptocrystalline; Cleavage: none (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed via the accumulation of silica-rich organic remains or chemical precipitation in marine environments. Often found as nodules or layered beds in carbonate rocks like limestone.

Uses & Applications

Historically used for stone tools (knapping); currently used in landscaping, as gemstones/jewelry when polished, and in some industrial grinding applications.

Geological Facts

Red chert is often called Jasper when it is opaque. Its conchoidal fracture creates extremely sharp edges, which led to its widespread use for arrowheads and scrapers by ancient civilizations.

Field Identification & Locations

Identify by its smooth, waxy surface and shell-like (conchoidal) fracture pattern. It will easily scratch glass but cannot be scratched by a steel knife. Common in sedimentary basins worldwide.

Identified on: 5/1/2026

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