sedimentary
Chert (Flint)
Silicon Dioxide (SiO2) - Microcrystalline Quartz
Hardness: 7 Mohs scale; Color: Cream, tan, grey, or brown; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 Mohs scale
- Color
- Cream, tan, grey, or brown
- Luster
- Waxy to vitreous
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Physical properties
Hardness: 7 Mohs scale; Color: Cream, tan, grey, or brown; Luster: Waxy to vitreous; Crystal structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation in marine environments; often occurs as nodules in limestone or chalk beds. Geological age ranges from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads); currently used in road construction, as an abrasive, and occasionally in jewelry as cabochons.
Geological facts
Due to its conchoidal fracture, it produces extremely sharp edges. It was the primary material for the 'Stone Age' technology and can create sparks when struck against steel, which was used in early firearms like flintlocks.
Field identification & locations
Identify by its 'shell-like' curved (conchoidal) fractures and its ability to scratch glass. It feels smooth and waxy to the touch. Commonly found in riverbeds or eroding out of limestone cliffs in places like the UK, USA (Ohio, Texas), and France.
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