Where is Fossiliferous Chert found?
Sedimentary rock (Chert with fossil inclusions)
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Open the appFossiliferous Chert occurs in specific geological environments. Knowing where to look, and in what kind of rock, is the difference between going home empty-handed and finding a great specimen.
Where to find Fossiliferous Chert
North America
Widespread in various Paleozoic and Mesozoic formations across the United States (e.g., Burlington Limestone in the Midwest, Monterey Formation in California, Arkansas Novaculite) and Canada.
Europe
Common in the Chalk Group of England and France, and in various Alpine and Mediterranean Mesozoic and Cenozoic sequences.
Asia
Found in numerous locations, particularly in ancient marine sedimentary basins, such as those in Japan, China, and Russia.
Australia
Occurs in various sedimentary successions, including those with ancient radiolarian cherts.
Collecting tips
- Look for Outcrops. Search for exposures in road cuts, stream beds, quarries, and coastal cliffs where sedimentary rocks are visible. Chert often forms resistant layers or nodules that stand out from softer surrounding rocks.
- Examine Associated Rocks. Fossiliferous chert is commonly found interbedded with or as nodules within limestones, shales, and mudstones. Identifying these associated rock types can lead to chert discoveries.
- Check for Conchoidal Fracture. Freshly broken chert will exhibit a characteristic conchoidal (shell-like) fracture, which is a key identifying feature. Look for sharp, curved edges.
- Inspect for Fossils. Carefully examine the rock surface and fresh breaks for visible fossil remains. A hand lens or magnifying glass can be very useful for identifying smaller inclusions.
- Acid Test (Caution). While chert itself does not react with dilute hydrochloric acid, any calcareous fossils within it might. A small drop of 10% HCl can be applied to a fossil inclusion (if visible) to check for effervescence, indicating a calcareous composition that has been preserved or partially replaced. Always exercise caution and wear appropriate safety gear when handling acids.
Quick Check
- Color:
- Variable (white, gray, black, brown, red, green)
- Luster:
- Dull to waxy, vitreous on fresh fracture
- Streak:
- White
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