Chert (often called Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: Brown, gray, or tan; Luster: Waxy to vitreous; Crystal Structure: Microcrystalline; Cleavage: None (conchoidal fracture); Specific Gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic debris (like diatoms or radiolarians) or chemical precipitation from groundwater within limestone or chalk beds.

Uses & Applications

Historically used for stone tools (knapping) and fire-starting. Currently used in road surfacing, as abrasive material, and occasionally for decorative landscaping.

Geological Facts

Chert was one of the most important minerals to prehistoric humans because it breaks with sharp, predictable edges, making it ideal for arrowheads and scrapers.

Field Identification & Locations

Identify by its waxy appearance and conchoidal (shell-like) fracture patterns that produce sharp edges. It will easily scratch glass. Commonly found in limestone outcrops and riverbeds.

Identified on: 4/19/2026

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