sedimentary
Chert (Green variety)
Microcrystalline Quartz (SiO2)
Hardness: 7 on Mohs scale; Color: Green, teal, and cream; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
- Hardness
- 7 on Mohs scale
- Color
- Green, teal, and cream
- Luster
- Waxy to dull
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Physical properties
Hardness: 7 on Mohs scale; Color: Green, teal, and cream; Luster: Waxy to dull; Crystal structure: Cryptocrystalline; Cleavage: None (conchoidal fracture); Specific gravity: 2.65
Formation & geological history
Formed through the accumulation of silica-rich microfossils (like radiolarians or diatoms) or by precipitation from silica-rich fluids in limestone or shale. Often dates from the Paleozoic or Mesozoic eras.
Uses & applications
Historically used for stone tools (arrowheads) due to its sharp fracture. Currently used for lapidary work, jewelry, and as decorative river rock.
Geological facts
Chert is so hard it can strike sparks against steel. The green coloration often comes from trace inclusions of minerals like chlorite or celadonite.
Field identification & locations
Identify in the field by its smooth, waxy texture and shell-like (conchoidal) curved fractures. Common in riverbeds and coastal deposits worldwide, especially in areas with tectonic uplift.
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