Chert (Nodule/Common Chert)

Physical Properties

Hardness: 6.5-7 (Mohs scale), Color: tan to light grey with tan patina, Luster: waxy to dull, Crystal structure: cryptocrystalline, Cleavage: none (conchoidal fracture), Specific gravity: 2.5-2.8

Formation & Geological History

Formed through the accumulation of silica-rich organic remains or chemical precipitation within limestone or chalk beds, often during the Paleozoic or Mesozoic eras.

Uses & Applications

Historically used for stone tools (arrowheads); currently used in road construction, as an abrasive, and sometimes in landscaping.

Geological Facts

Chert is so hard it can create sparks when struck against steel. It was one of the most vital materials for prehistoric humans due to its ability to hold a sharp edge.

Field Identification & Locations

Identify by its waxy luster, conchoidal (shell-like) fracture, and the fact it can scratch steel or glass. Commonly found as nodules in limestone outcrops or as river stones.

Identified on: 5/9/2026

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