sedimentary
Chert (Flint)
Silicon Dioxide (SiO2)
Hardness: 7 (Mohs scale); Color: tan, brown, grey, yellowish; Luster: waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: none; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- tan, brown, grey, yellowish
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: tan, brown, grey, yellowish; Luster: waxy to dull; Crystal structure: Cryptocrystalline (microscopic quartz); Cleavage: none; Fracture: Conchoidal (shell-like curves); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolaria or diatoms) or by chemical precipitation from groundwater. Often found as nodules within limestone or chalk beds. Age can vary from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons. Currently used as a road surfacing material, in construction aggregate, and occasionally in jewelry as or lapidary art when colorful (Jasper/Agate variants).
Geological facts
Chert was one of the most important minerals for early humans because of its ability to break into sharp edges. It is chemically very stable and resistant to weathering.
Field identification & locations
Identify by its 'shell-like' curved fractures, waxy appearance, and extreme hardness (it will easily scratch glass). Look for it in limestone outcrops or as rounded river cobbles.
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