Chert (varieties include Flint or Jasper)

Physical Properties

Hardness: 7 on Mohs scale; Color: Tan, beige, or white; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); 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 from silica-rich fluids within other sedimentary rocks like limestone. Common in Paleozoic and Mesozoic strata.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) due to sharp edges; currently used in construction aggregate, road surfacing, and as a raw material for ceramics.

Geological Facts

Chert nodule formation often replaces carbonate minerals. It was one of the most vital materials for early humans because its conchoidal fracture produces edges sharper than a steel scalpel.

Field Identification & Locations

Identify in the field by its hardness (it will scratch glass), smooth waxy feel, and curved 'clamshell' fracture patterns. Often found as nodules or layers within limestone beds.

Identified on: 4/20/2026

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