ruby said:

Michael V said:

ruby said:

Oh, lovely detail. The fellow is a retired chemical nerd so he’ll like this.

What made the curious looking indentations in the first picture? Everyone that saw the pics of course said ‘aliens’. Excluding the possibilty of little green Martians seeing a tempting piece of damp iron deposits and writing the Martian equivalent of Foo was here, how would this form?

The words ironstone concretions….I take it the iron has some of the surrounding rock mixed in with it?

OK, the rock was porous. The “rust” was deposited in the gaps between grains. The concentric “layers” are slight variations between deposition episodes. Weathering has visually enhanced these differences. This more obvious in the second photo.

The strange-looking first rock contains multiple centres of ironstone deposition that eventually all joined together and became encapsulated in the outer layers. Then it was weathered.

Get the chemical guy to look up Eh-pH interfaces, sandstone porosity, meteoric water, and of course, ironstone concretions.

:)

Ha, now I have more questions, but I think that will suffice, as you have given ME some interesting things to look up too.
You rock MV :)))

:)