Has anyone come accross rocks like this?

Like this?

At least it's not a copralite.

Yes, thats the stuff hAyyoUinAu.

Hi hAyyoUinAu, the iron concretions are very common all over the world. The iron is mobilised in the soil/regolith/weathered buried rocks and forms concretions around rocks or migrates/leaches outward in a rock forming a sphere. The inside rock rots away leaving the hardened iron shell.

The process while it looks like heat is involved all happens at room temperature. I think most of the nodules in Austarlia now found laying on the surface all formed in the soil during a wetter warmer climate in the Tertiary period or earlier.

I found a batch that were sealed nodules and they contained beautiful evaporate minerals/needle crtstals of gypsum etc.

If you google "liesegang rings" it will tell you about the iron being mobilised.

The one below attached my attention and is in the garden now. It is over 12 inches in width. The total nodule was over 2.5 feet in diameter.
Cheers RDD

at least you all know one thing...... its a rock hahaha

Thanks RedDirtDigger, and that is a beautiful speci.