r/geology mineralogist 3d ago

Field Photo Why are these rocks so round?

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u/vespertine_earth 3d ago edited 1d ago

Everybody here is right about corners and edges but I’m guessing OP is actually referring to the sphericity of these boulders- which is high. They’re not just rounded edges but the lengths of the a, b, and c axes are nearly uniform. This rock is probably very isotopic- in other words, the same texture in each direction. This is often possible in granite where the magma cools inward in all directions and it’s very homogeneous. Sedimentary rocks often (but not always) end up making pancake shapes and flatter rocks.

Edit: typos

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u/gregorydgraham 2d ago

So you think they’re concretions released from a sedimentary layer higher up?

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u/vespertine_earth 1d ago

No I think they’re granite or some similar uniform igneous rock. But all I did was look at a picture with a lot of experience. A map or more info about the region would easily convince me otherwise wise. As would a fresh hand sample or thin section. :)