Chert (Flint)

Physical Properties

Hardness: 7 (Mohs scale); Color: Gray, tan, or brown; Luster: Waxy to dull; Crystal structure: Hexagonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Formation & Geological History

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation from groundwater within sedimentary beds. Most common in limestone or chalk deposits.

Uses & Applications

Historically used for stone tools (arrowheads, scrapers) due to its sharp edges; modern uses include road surfacing, jewelry (as jasper), and flint-starting tools.

Geological Facts

Chert has been used by humans for hundreds of thousands of years for tool-making because it breaks into predictably sharp, glass-like edges. It is extremely chemically stable and resistant to weathering.

Field Identification & Locations

Identify in the field by its waxy texture, inability to be scratched by steel, and unique conchoidal (shell-like) fracture patterns. Frequently found in riverbeds or eroding out of limestone cliffs.

Identified on: 4/28/2026

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