sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale); Color: tan, brown, yellow-brown; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none, exhibits conchoidal fracture.
- Hardness
- 7 (Mohs scale)
- Color
- tan, brown, yellow-brown
- Luster
- waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: tan, brown, yellow-brown; Luster: waxy to dull; Crystal structure: Trigonal (microscopic); Cleavage: none, exhibits conchoidal fracture.
Formation & geological history
Formed through the accumulation of silica-rich microfossils or via chemical precipitation in sedimentary basins as modules or lenses. Age varies widely from Precambrian to Cenozoic era.
Uses & applications
Historically used for making stone tools (arrowheads). Modernly used in lapidary work, jewelry (tumbled stones), and as road ballast or construction aggregate.
Geological facts
Chert is so hard it can strike sparks from steel, which led to its use in flintlock firearms. It was one of the most vital materials for early human survival for making sharp blades.
Field identification & locations
Identify in the field by its waxy luster, smoothness, and distinct shell-like (conchoidal) curves where it is broken; it is harder than a steel knife blade. Common in limestone regions.
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