Liesegang rings (geology)

Liesegang rings (/ˈliːzəɡɑːŋ/) (also called Liesegangen rings or Liesegang bands) are colored bands of cement observed in sedimentary rocks that typically cut across bedding. These secondary (diagenetic) sedimentary structures exhibit bands of (authigenic) minerals that are arranged in a regular repeating pattern. Liesegang rings are distinguishable from other sedimentary structures by their concentric or ring-like appearance. The precise mechanism from which Liesegang rings form is not entirely known and is still under research, but there is a precipitation process that is thought to be the catalyst for Liesegang ring formation, referred to as the Ostwald-Liesegang supersaturation-nucleation-depletion cycle. Though Liesegang rings are considered a frequent occurrence in sedimentary rocks, rings composed of iron oxide can also occur in permeable igneous and metamorphic rocks that have been chemically weathered.