sedimentary
Chert (specifically Flint or Jasper variant)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Dark brown to black with banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Dark brown to black with banding
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Dark brown to black with banding; Luster: Waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of siliceous remains of organisms (like diatoms or radiolarians) or chemical precipitation from silica-rich fluids in sedimentary basins. Specimens can range from Precambrian to Recent geological ages.
Uses & applications
Historically used for stone tools (arrowheads/scrapers) and fire-starting. Currently used as an abrasive, in construction aggregate, and as a semi-precious gemstone for jewelry (cabochons) or decorative carvings.
Geological facts
Chert was one of the first materials utilized by early humans for tool-making because of its predictable conchoidal fracture which creates razor-sharp edges. Gunflint was a critical industrial supply for flintlock firearms for centuries.
Field identification & locations
Identify in the field by its smooth, shell-like (conchoidal) fracture surfaces and its ability to scratch glass. It is commonly found as nodules in limestone or chalk beds. Collectors look for unique banding patterns or colors.
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