sedimentary
Chert / Flint
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale. Color: Highly variable, typically grey, black, or brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic silica crystals). Cleavage: None (exhibits conchoidal/shell-like fracture). Specific gravity: 2.65.
- Hardness
- 7 on Mohs scale
- Color
- Highly variable, typically grey, black, or brown
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale. Color: Highly variable, typically grey, black, or brown. Luster: Waxy to dull. Crystal structure: Cryptocrystalline (microscopic silica crystals). Cleavage: None (exhibits conchoidal/shell-like fracture). Specific gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like radiolarians or diatoms) or by chemical precipitation in marine environments. It can form as nodules in limestone or chalk beds. Geological age ranges from Precambrian to Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads, scrapers) due to its sharp edges. Currently used in road construction, as an abrasive, and sometimes in jewelry (as jasper or flint).
Geological facts
Because of its ability to produce sparks when struck against steel, it was the primary ignition source for flintlock firearms for centuries. It breaks into glass-sharp edges that are still used in some specialized surgical scalpels.
Field identification & locations
Identify in the field by its very smooth, glass-like fracture surfaces and extreme hardness (it will scratch glass). It is commonly found in riverbeds, glacial till, and embedded in limestone cliffs. It is a favorite for lapidary tumbling.
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