Where is Chert found?
Chert (cryptocrystalline quartz)
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Open the appChert 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 Chert
North America
Abundant in many Paleozoic and Mesozoic carbonate sequences, such as the Burlington Limestone (Midwest USA), Fort Payne Formation (southeastern USA), and various chert-rich units in the Appalachian and Ouachita Mountains. Novaculite is found in Arkansas and Oklahoma.
Europe
Flint is very common in the chalk formations of England (e.g., Dover Cliffs), France, and other parts of Western Europe. Chert beds are also found in various sedimentary basins.
Asia
Significant chert deposits are found in the Tethyan sedimentary sequences, particularly in regions like the Himalayas and Southeast Asia, often associated with ancient ocean basins.
Australia
Chert is present in various sedimentary successions, including Precambrian banded iron formations and younger marine deposits.
Collecting tips
- Look in Carbonate Rocks. Chert nodules and beds are frequently found interbedded with or replacing limestone and dolomite. Examine outcrops of these rocks for hard, dense, often darker-colored inclusions.
- Check Stream Beds and Gravel Pits. Due to its hardness and resistance to weathering, chert often accumulates in stream beds, river gravels, and glacial till. Look for smooth, rounded, dense pebbles and cobbles.
- Examine Road Cuts and Construction Sites. Fresh exposures of sedimentary rock layers, such as those found in road cuts or construction excavations, can reveal chert layers or nodules.
- Look for Conchoidal Fracture. A key identifying feature is the conchoidal (shell-like) fracture, which produces sharp, curved edges. This is often visible on broken pieces.
- Test Hardness. Chert is hard (Mohs 7) and will scratch glass and steel. This helps distinguish it from softer rocks.
Quick Check
- Color:
- Variable (white, gray, black, brown, red, green)
- Luster:
- Waxy to dull, sometimes vitreous
- Streak:
- White
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