Where is Chert in Sandstone found?
Sedimentary rock with chert nodules/fragments
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Open the appChert in Sandstone 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 in Sandstone
Appalachian Basin, USA
Numerous Paleozoic formations, such as the Oriskany Sandstone, contain chert fragments derived from older chert beds.
Ouachita Mountains, USA
Mississippian and Pennsylvanian sandstones often contain abundant chert clasts derived from the erosion of novaculite and other chert formations.
Western Australia
Proterozoic and Phanerozoic sedimentary sequences, including some iron formations, can contain chert-rich sandstones.
Europe (e.g., UK, France)
Cretaceous and Jurassic sandstones, particularly those associated with marine transgressions, may contain chert nodules or fragments.
Collecting tips
- Look for Hardness Contrast. Chert is significantly harder than most sandstone matrix minerals (except quartz). On weathered surfaces, chert nodules or fragments often stand out in relief due to their greater resistance to erosion.
- Examine Fracture Patterns. Chert typically exhibits a conchoidal (shell-like) fracture, which is distinct from the granular fracture of most sandstones. Look for these characteristic breaks within the embedded components.
- Check for Biogenic Remains. If the chert is biogenic in origin, microscopic examination might reveal fossilized radiolarians, diatoms, or sponge spicules within the chert components, though this is not always visible to the naked eye.
- Consider Geological Context. Chert-bearing sandstones are often found in regions with a history of marine sedimentation, particularly where silica-rich organisms thrived or where volcanic ash was deposited and subsequently silicified.
Quick Check
- Color:
- Variable (sandstone matrix typically light, chert can be any color)
- Luster:
- Dull to waxy to vitreous
- Streak:
- White
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