sedimentary
Chert (Green variety)
Chert (Silicon Dioxide, SiO2)
Hardness: 7 (Mohs scale); Color: Pale green, grey, and tan; Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
- Hardness
- 7 (Mohs scale)
- Color
- Pale green, grey, and tan
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 (Mohs scale); Color: Pale green, grey, and tan; Luster: Waxy to dull; Structure: Cryptocrystalline (microscopic quartz crystals); Cleavage: None (conchoidal fracture); Specific Gravity: 2.65.
Formation & geological history
Formed through the accumulation of silica-rich organic remains (diatoms/radiolarians) or chemical precipitation from silica-rich fluids in ocean basins. These rocks can range from Precambrian to Cenozoic in age.
Uses & applications
Historically used for making sharp tools like arrowheads. Modernly used in road construction as aggregate, landscaping, and lapidary work for cabochons and jewelry.
Geological facts
Chert is so hard that it can strike sparks against steel, a property that was used for firearms and fire-starting for centuries. Green chert often gets its color from chlorite or iron inclusions.
Field identification & locations
Identify by its extreme hardness (cannot be scratched by a steel knife) and its smooth, shell-like (conchoidal) fracture surfaces. Commonly found in limestone or dolostone beds.
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