Where is Banded Chert found?
Chert (sedimentary rock)
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Open the appBanded 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 Banded Chert
North America
Extensive chert deposits are found in the Ouachita Mountains (Arkansas, Oklahoma), Appalachian Mountains, and throughout the midwestern United States (e.g., Burlington Chert in Missouri, Indiana). Flint Ridge in Ohio is famous for its high-quality banded flint. The Monterey Formation in California contains significant chert beds.
Europe
Flint nodules are common in Cretaceous chalk formations across England (e.g., Dover Cliffs), France, and other parts of Western Europe. Radiolarite cherts are found in the Alps and Mediterranean regions.
Australia
Banded cherts are present in various Precambrian and Paleozoic successions, often associated with banded iron formations or deep-marine sediments.
Africa
Significant chert occurrences are found in the ancient cratons, often associated with early life forms (stromatolites) and banded iron formations.
Collecting tips
- Look for outcrops in sedimentary sequences. Chert often forms as distinct beds or nodules within limestone, shale, or chalk formations. Look for resistant layers that stand out from softer surrounding rocks.
- Examine stream beds and gravel pits. Due to its hardness and resistance to weathering, chert fragments are commonly found in river gravels, glacial tills, and alluvial deposits.
- Check for conchoidal fracture. A fresh break on chert will typically show a smooth, curved, shell-like fracture surface, which is a key diagnostic feature.
- Observe banding patterns. For banded chert specifically, look for parallel layers of differing colors or textures. This can be more evident on weathered surfaces or freshly broken pieces.
Quick Check
- Color:
- Variable, often banded (white, gray, black, brown, red, green)
- Luster:
- Dull to waxy to vitreous
- Streak:
- White
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