sedimentary
Chert (Jasper/Flint variety)
Microcrystalline or Cryptocrystalline Quartz (SiO2)
Hardness: 6.5-7 on Mohs scale; Color: tan, brown, or buff; Luster: dull to waxy; Structure: cryptocrystalline (microscopic crystals); Cleavage: none, breaks with conchoidal (shell-like) fracture.
- Hardness
- 6
- Color
- tan, brown, or buff
- Luster
- dull to waxy
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Physical properties
Hardness: 6.5-7 on Mohs scale; Color: tan, brown, or buff; Luster: dull to waxy; Structure: cryptocrystalline (microscopic crystals); Cleavage: none, breaks with conchoidal (shell-like) fracture.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (like diatoms or radiolaria) or the chemical replacement of limestone/dolomite. This specimen likely originates from a terrestrial bank or riverbed where it has undergone mechanical weathering.
Uses & applications
Historically used for making stone tools (arrowheads, scrapers) due to its sharp edges. Modernly used as road aggregate, in landscaping, and occasionally as a semi-precious gemstone when colorful (Jasper).
Geological facts
Chert is so hard it can strike sparks against steel, which is why the variety known as 'flint' was essential for early firearms and fire-starting. It is incredibly durable and resistant to chemical weathering.
Field identification & locations
Identify in the field by its hardness (it will scratch glass) and its smooth, curved 'conchoidal' fracture patterns. Commonly found in stream beds or as nodules within limestone layers.
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