Chert (specifically Red Chert or Jasper)

Physical Properties

Hardness: 6.5-7 on Mohs scale; Color: Reddish-brown to orange-brown; Luster: Waxy to dull; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.6-2.7.

Formation & Geological History

Formed via the accumulation of silica-rich organic remains (like radiolaria or diatoms) or chemical precipitation from silica-rich fluids in ocean basins. This specimen likely formed in a marine environment and underwent compaction and lithification over millions of years.

Uses & Applications

Historically used for making stone tools (arrowheads, scrapers) due to its conchoidal fracture. Today used for lapidary work, decorative landscaping, and as a collector's specimen. Red varieties are often polished for jewelry as Jasper.

Geological Facts

Chert is so hard it can create sparks when struck against steel, which made it vital for flintlock firearms. The red color is typically due to the inclusion of iron oxide (hematite) within the silica matrix.

Field Identification & Locations

Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces that are sharp enough to cut skin. It cannot be scratched by a steel knife. Commonly found in limestone or chalk beds as nodules.

Identified on: 5/1/2026

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