sedimentary
Green Chert
Microcrystalline Quartz (SiO2)
Hardness: 7 (Mohs scale), Color: dull green to sage with banding, Luster: waxy to vitreous, Structure: microcrystalline/cryptocrystalline, Specific Gravity: 2.65
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Physical properties
Hardness: 7 (Mohs scale), Color: dull green to sage with banding, Luster: waxy to vitreous, Structure: microcrystalline/cryptocrystalline, Specific Gravity: 2.65
Formation & geological history
Formed primarily through the accumulation of silica-rich organic remains (like diatoms or radiolarians) or chemical precipitation from hydrothermal fluids in marine environments. Often associated with the Franciscan Complex or similar oceanic seafloor sequences.
Uses & applications
Historically used for making stone tools (lithics) due to its conchoidal fracture. Today used for lapidary work, landscaping, and as a collector's specimen.
Geological facts
Green chert is a primary component of the Monterey and Franciscan formations in California. It is often found near plate boundaries where oceanic sediments have been scraped off and accreted onto a continent.
Field identification & locations
Identify by its characteristic conchoidal (shell-like) fracture, extreme hardness (scratches glass), and waxy feel. Common in riverbeds and coastal regions near tectonic subduction zones.
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