Liesegang rings (geology)
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Liesegang rings (/ˈliːzəɡɑːŋ/) (also called Liesegangen rings or Liesegang bands) are colored bands of cement observed in sedimentary rocks that typically cut across bedding.[1][2] These secondary (diagenetic) sedimentary structures exhibit bands of (authigenic) minerals that are arranged in a regular repeating pattern.[3] 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,[4] 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.[5] Though Liesegang rings are considered a frequent occurrence in sedimentary rocks,[6] rings composed of iron oxide can also occur in permeable igneous and metamorphic rocks that have been chemically weathered.[7]