Liesgang rings

Liesgang rings are a secondary diagenetic structures, the process of their formation is not compeletly understood.

It appeared that they formed by the iron oxides and their minerals during weathering. One of the common mechanisms proposed by geochemists is that Liesegang rings develop when there is a lack of convection and have a relationship to intermodulation of interacting species such as oxygen and ferrous iron that precipitate in separate discrete bands that become divergent in a geometric pattern.