Chert (Fossiliferous)

Physical Properties

Hardness: 7 (Mohs scale), Color: Tan to brown, Luster: Dull to waxy, Crystal structure: Microcrystalline (cryptocrystalline), Fracture: Conchoidal, Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or sponges) on the seafloor, often replacing original limestone through chemical precipitation. Frequently found in Paleozoic or Mesozoic strata.

Uses & Applications

Historically used for stone tools (arrowheads); currently used as road aggregate, in landscaping, and as a collector's specimen if fossils are present.

Geological Facts

Chert is so hard it can strike sparks from steel. Specimens like this often contain micro-fossils of ancient marine life such as crinoids, shells, or bryozoans.

Field Identification & Locations

Identify in the field by its hardness (cannot be scratched by a steel blade) and its smooth, shell-like fracture surfaces. Look for it in limestone basins or river gravels.

Identified on: 4/19/2026

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