sedimentary
Chert (Flint)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
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
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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.
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