Chert (specifically White Chert or Flint)

Physical Properties

Hardness: 7 (Mohs), Color: Cream, white, or light tan, Luster: Waxy to vitreous, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.6-2.7

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 to Mesozoic strata.

Uses & Applications

Historically used for stone tools (arrowheads). Today used as a decorative stone, road surfacing, and sometimes in porcelain manufacturing or as a gemstone in the form of Jasper/Agate.

Geological Facts

Chert produces sparks when struck against steel, which made it a critical survival tool for making fire throughout human history. It is one of the most durable sedimentary rocks due to its high silica content.

Field Identification & Locations

Identify in the field by its very smooth, waxy surface and its sharp, shell-like (conchoidal) fracture edges. It cannot be scratched by a steel knife. Commonly found in riverbeds or as nodules within limestone outcrops.

Identified on: 5/9/2026

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