sedimentary

Chert (Flint)

Microcrystalline silica (SiO2)

Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, gray, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Hardness: 6
Color: Tan, brown, gray, or black
Luster: Waxy to dull

Identified June 25, 2026More sedimentary →

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Physical properties

Hardness: 6.5-7 (Mohs scale); Color: Tan, brown, gray, or black; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.5-2.8

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments. Often found as nodules in limestone or chalk beds.

Uses & applications

Historically used for stone tools and weapons due to sharp edges; currently used in construction aggregate, as a fire-starter (flint), and for decorative carvings or jewelry.

Geological facts

Chert was one of the most important raw materials for prehistoric humans to create arrowheads and scrapers. The word 'flint' is often reserved for chert found in chalk or marly limestone.

Field identification & locations

Identify by its waxy luster, smooth conchoidal (shell-like) fracture, and extreme hardness (it will scratch glass). Commonly found in stream beds or weathered out of limestone cliffs.