sedimentary

Chert (Chert / Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

Hardness: 7 on Mohs scale; Color: Gray, tan, or bluish-gray; Luster: Dull or waxy until polished; Crystal structure: Trigonal (microscopic); Cleavage: None (exhibits prominent conchoidal fracture); Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, or bluish-gray
Luster: Dull or waxy until polished

Identified March 8, 2026More sedimentary →

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Physical properties

Formation & geological history

Formed through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or through the chemical precipitation of silica in groundwater. Often found as nodules within limestone or chalk beds, primarily from the Paleozoic and Mesozoic eras.

Uses & applications

Historically used for stone tools and weapons (arrowheads) due to its sharp edges; modernly used as road aggregate, in jewelry (when decorative), and as a component in ceramics.

Geological facts

The conchoidal fracture pattern seen in this specimen (the dish-like chips) is exactly how prehistoric humans shaped tools. Flint is a specific variety of dark chert found in chalk or marly limestone.

Field identification & locations

Identify in the field by its superior hardness (scratches glass), waxy feel, and the distinctive 'scooped out' appearance of broken surfaces (conchoidal fracture). Commonly found in riverbeds or eroding out of limestone cliffs.

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