sedimentary
Fossiliferous Chert or Agate
Microcrystalline quartz (SiO2) with fossiliferous inclusions
Hardness of 7 on the Mohs scale; colors range from greyish-brown to translucent with white fossil inclusions; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture; specific gravity around 2.60 to 2.65.
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Physical properties
Hardness of 7 on the Mohs scale; colors range from greyish-brown to translucent with white fossil inclusions; waxy to vitreous luster; cryptocrystalline structure; conchoidal fracture; specific gravity around 2.60 to 2.65.
Formation & geological history
Formed through the replacement of limestone or other carbonate rocks by silica-rich groundwaters over millions of years, often preserving ancient organic or fossil structures in marine environments.
Uses & applications
Collected by rockhounds, lapidary work, decorative display specimens, and historical use for stone tools.
Geological facts
Chert and flint often preserve microfossils and trace fossils of ancient marine life, providing key insights into prehistoric ecosystems.
Field identification & locations
Found commonly in limestone formations, riverbeds, and coastal beaches where water has weathered out resistant nodules. Identify by its high hardness, conchoidal fracture, and distinctive fossil patterns.
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