sedimentary
Chert / Flint
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on the Mohs scale. Color: Gray, black, or blue-gray. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic fibers). Cleavage: None (exhibits conchoidal fracture). Specific Gravity: 2.6 – 2.65.
- Hardness
- 7 on the Mohs scale
- Color
- Gray, black, or blue-gray
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on the Mohs scale. Color: Gray, black, or blue-gray. Luster: Waxy to dull. Crystal structure: Trigonal (microscopic fibers). Cleavage: None (exhibits conchoidal fracture). Specific Gravity: 2.6 – 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or chemical precipitation in marine environments. It is often found as nodules in limestone or chalk beds. Geological age ranges from the Precambrian to the Cenozoic.
Uses & applications
Historically used for stone tools and weapons (arrowheads, knives) due to its sharp edges. Modern uses include abrasives, construction aggregates, and occasionally as semi-precious gemstones for jewelry or decorative carvings.
Geological facts
Because it creates hot sparks when struck against steel, it was the primary ignition source for flintlock firearms. It is one of the toughest common materials used by early humans for tool development.
Field identification & locations
Identify in the field by its characteristic smooth, curved (conchoidal) fracture surfaces and sharp edges when broken. It cannot be scratched by a steel knife. Commonly found in limestone outcrops, riverbeds, and coastal cliffs in regions like the UK, France, and North America.
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