sedimentary
Chert (Green Chert or Jasper)
Microcrystalline Quartz (SiO2)
Hardness 6.5-7 on Mohs scale; Color: olive green to dark green; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves); Specific gravity: 2.58-2.91.
- Color
- olive green to dark green
- Luster
- waxy to dull
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Physical properties
Hardness 6.5-7 on Mohs scale; Color: olive green to dark green; Luster: waxy to dull; Crystal structure: cryptocrystalline; Cleavage: none; Fracture: conchoidal (shell-like curves); Specific gravity: 2.58-2.91.
Formation & geological history
Formed from the accumulation of silica-rich organic remains (like radiolarians or diatoms) or chemical precipitation in marine environments. The green hue often results from iron or magnesium-rich silicates. Usually from the Phanerozoic eon.
Uses & applications
Historically used for stone tools and weapons due to sharp edges; currently used for lapidary work, jewelry, gravel, and collection.
Geological facts
Chert was one of the most important minerals for early humans because of its ability to fracture into surgical-sharp edges. Ancient arrowheads and scrapers are frequently found made from this material.
Field identification & locations
Identify by its 'glassy' conchoidal fracture patterns upon breaking and its inability to be scratched by a steel knife. Commonly found in river beds and sedimentary deposits as nodules.
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