sedimentary
Chert (Flint/Jasper variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Tan, brown, and grey banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Tan, brown, and grey banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65.
Formation & geological history
Formed in marine or freshwater environments through the chemical precipitation of silica or the accumulation of siliceous skeletal remains (like radiolaria or diatoms). Over geological time, these sediments undergo diagenesis and petrification.
Uses & applications
Historically used for stone tools and weapons (arrowheads) due to its sharp edges; modernly used in road construction, as a decorative garden stone, and occasionally in jewelry as Jasper.
Geological facts
Chert has a conchoidal fracture, meaning it breaks like glass to create razor-sharp edges. Famous variants like Flint were essential for prehistoric human survival, while the 'Jasper' variety is prized by lapidaries.
Field identification & locations
Identify it in the field by its hardness (it will easily scratch glass) and the shell-like (conchoidal) curves on broken faces. Commonly found in limestone or chalk beds. Collectors look for unique banding patterns or colors.
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