sedimentary

Chert (Flint)

Microcrystalline or Cryptocrystalline Quartz (SiO2)

AI-generated identification · may be incorrect

Hardness: 7 on Mohs scale; Color: Gray, tan, brown with waxy luster; Crystal structure: Trigonal (microcrystalline); Conchoidal fracture; Specific gravity: 2.65.

Hardness: 7 on Mohs scale
Color: Gray, tan, brown with waxy luster

Identified July 19, 2026More sedimentary →

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Physical properties

Hardness: 7 on Mohs scale; Color: Gray, tan, brown with waxy luster; Crystal structure: Trigonal (microcrystalline); Conchoidal fracture; Specific gravity: 2.65.

Formation & geological history

Formed primarily from the accumulation of silica-rich skeletal remains (like diatoms or radiolarians) in marine environments, or through chemical precipitation in limestone or chalk beds.

Uses & applications

Historically used for stone tools (knapping) and fire-starting; currently used as a road aggregate, in jewelry (when decorative), and for abrasive purposes.

Geological facts

Chert has been used by humans for over 2 million years to create sharp-edged tools like arrowheads and knives because of its predictable conchoidal fracture.

Field identification & locations

Identified by its extreme hardness (scratches glass), waxy texture when broken, and curved fracture patterns. Found globally in sedimentary rock sequences, especially within limestone layers.