Where is Chert found?
Sedimentary rock (chemical)
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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
United States
Widespread, particularly in the Appalachian Mountains, Ozark Plateau (Arkansas Novaculite), and throughout the Midwest in Mississippian and Pennsylvanian limestones. Flint is common in Cretaceous chalks of Kansas and Texas.
United Kingdom
Flint is abundant in the Cretaceous chalk formations, especially along the southern and eastern coasts (e.g., Dover cliffs).
France
Flint is common in Cretaceous chalks, particularly in the Paris Basin and northern regions.
Australia
Found in various sedimentary basins, often associated with ancient marine deposits.
Russia
Occurs in numerous sedimentary sequences across the vast landmass.
Collecting tips
- Look in Carbonate Rocks. Chert often forms as nodules or layers within limestone and dolomite. Examine outcrops of these rocks for distinct, harder, and often darker inclusions.
- Check Riverbeds and Gravel Pits. Due to its hardness and resistance to weathering, chert is a common component of river gravels, glacial till, and alluvial deposits. Look for angular to sub-rounded, dense, fine-grained pebbles.
- Examine Fracture Surfaces. A key identifying feature is its conchoidal (shell-like) fracture, which produces sharp, curved surfaces. This is distinct from the planar cleavage of many other minerals.
- Test Hardness. Chert is hard (Mohs 7) and will scratch glass and most common metals. This helps distinguish it from softer rocks like limestone.
- Observe Color and Luster. While variable, the dull to waxy luster and often uniform color (or subtle banding) can be indicative. Flint is typically dark gray to black.
Quick Check
- Color:
- Variable (white, gray, black, brown, red, green, yellow)
- Luster:
- Dull to waxy
- Streak:
- White
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