sedimentary

Chert (Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

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

Hardness: 7 on Mohs scale
Color: Gray, brown, tan, or black
Luster: Waxy to dull

Identified March 22, 2026More sedimentary →

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Physical properties

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

Formation & geological history

Formed through the accumulation of siliceous remains of marine organisms (like diatoms or radiolaria) or via chemical precipitation from silica-rich fluids in limestone or chalk beds. Often found in nodules or bedded layers.

Uses & applications

Historically used for stone tools (arrowheads). Modernly used as road aggregate, in jewelry (when decorative like jasper), and as a spark-maker in survival fire-starting kits.

Geological facts

Chert has a conchoidal fracture, allowing it to break into razor-sharp edges. It was one of the most vital materials for early human technological development.

Field identification & locations

Identify in the field by its waxy texture and shell-like (conchoidal) curved breaks. It will easily scratch glass and produce sparks when struck against steel. Commonly found in limestone outcrops or riverbeds.