Ring around the Rock baby...

This remains my favorite sample of Liesegang banding.
Liesegang bands are frivolous additions to sedimentary rocks caused by the penetration -- evaporation -- penetration -- evaporation by water. Water that contains iron oxides leave red bands, and manganese oxides leave purple bands. Possibly, the same water has both iron and manganese, but the more mobile manganese oxide penetrates further. Bands can be found on layer surfaces or across layers. I note: my explanation doesn't agree with that on Wikipedia, but then there seems no consensus about these bands, so I prefer to go with my own opinion. Anyway, MY sample is prettier than THEIR sample!