Where is Concretion found?

Concretion 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 Concretion

Collecting tips

1. Look for contrasting hardness. Concretions are typically harder and more resistant to weathering than the surrounding host rock, causing them to stand out on eroded surfaces or stream beds.
2. Examine sedimentary layers. Concretions often form within specific sedimentary layers. Look for them in shales, siltstones, and fine-grained sandstones.
3. Check for nuclei. Many concretions form around a central nucleus. Breaking open a concretion (if permitted and safe) may reveal a fossil or mineral fragment at its core.
4. Observe shapes. Concretions exhibit characteristic shapes, from spherical and ovoid to discoidal and irregular. Recognize these forms to distinguish them from ordinary rock fragments.
5. Investigate weathered outcrops. Erosion often exposes concretions as they are more resistant. Look for them weathering out of cliffs, road cuts, and riverbanks.

Quick Check

Color:

Variable (brown, gray, black, red, yellow, white)

Luster:

Dull to earthy

Streak:

Variable, depending on composition (e.g., white for calcite, reddish-brown for iron oxides)

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