Chert (Chert Nodule)

Physical Properties

Hardness: 7 Mohs; Color: Grey, brown, white; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed by the accumulation and diagenesis of silica-rich organic remains or chemical precipitation within marine or land-based sedimentary layers like limestone or chalk. Many date from the Paleozoic or Mesozoic eras.

Uses & Applications

Used historically for stone tools (flintknapping), as an industrial abrasive, or as decorative gravel. Higher-grade colorful varieties are used in lapidary work.

Geological Facts

Flint is a variety of chert. Because of its conchoidal fracture, it was the primary material used by prehistoric humans to create sharp edges for arrowheads and scrapers.

Field Identification & Locations

Identify by its 'shell-like' curved fracture surfaces and its ability to scratch glass. Commonly found as nodules within limestone outcrops or along riverbeds and beaches.

Identified on: 5/3/2026

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