Chert (varieties: Flint or Jasper)

Physical Properties

Hardness: 7 (Mohs scale), Color: Dark brown to black with reddish-tan weathering crust, Luster: Waxy to dull, Crystal Structure: Microcrystalline, Cleavage: None (conchoidal fracture), Specific Gravity: 2.65

Formation & Geological History

Formed through the precipitation of silica-rich fluids in sedimentary environments (like limestone) or via the accumulation of siliceous organisms like diatoms and radiolarians. Often dates from the Paleozoic to Mesozoic eras.

Uses & Applications

Historically used for making stone tools (knapping) and as strike-a-lights for fire making. Currently used in road surfacing and as a lapidary material for decorative stones/jewelry.

Geological Facts

Because it breaks with a conchoidal fracture, it creates edges sharper than a surgeon's steel scalpel. Native Americans and early humans used these materials extensively for arrowheads and scrapers.

Field Identification & Locations

Identify in the field by its very hard surface (scratches glass), waxy luster, and shell-like (conchoidal) breaking pattern. Common in river beds and limestone outcrops.

Identified on: 4/15/2026

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