Chert (specifically Tan Chert or Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: Tan, brown, or buff; Luster: Dull to waxy; Crystal Structure: Microcrystalline/Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from silica-rich fluids within limestone or chalk beds. Often Paleozoic or Mesozoic in age.

Uses & Applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as a gemstone (Jasper/Agate variants), and for landscaping.

Geological Facts

Chert breaks with a conchoidal fracture, creating sharp edges which is why it was the primary material for prehistoric arrowheads and spear tips. It is extremely resistant to chemical weathering.

Field Identification & Locations

Identify in the field by its smooth, waxy feel and the way it breaks into curved, shell-like flakes. It will easily scratch glass. Found globally in nodules or layered beds within carbonate rocks.

Identified on: 4/15/2026

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