Vivianite in the News -"Wastewater: recover vivianite mineral, from lab to pilot scale -with Wetsus partner", 05/12/2023, Structure -"In pure end member vivianite all the iron is divalent, Fe 2+ , but there are two distinct sites in the structure that these ions can occupy. In the first site, the Fe 2+ is surrounded by four water molecules and two oxygens, making an octahedral group. In the second site, the Fe 2+ is surrounded by two water molecules and four oxygens, again making an octahedral group. The oxygens are part of the phosphate groups (PO4 3-), that are tetrahedral. The vivianite structure has chains of these octahedra and tetrahedra that form sheets perpendicular to the a-crystal axis. The sheets are held together by weak bonds, and that accounts for the perfect cleavage between them" (Wikipedia, mentioning .