(named in 1817 after the English mineralogist J. G. Vivian), a mineral, a hydrous ferrous phosphate: Fe3(PO4)2’ 8H2O. It crystallizes in a monoclinic system and occurs in powdery or dense masses. Vivianite has a hardness of 1.5-2.0 on the mineralogical scale, a density of 2,680-2,710 kg/m³, and a pale green color that turns blue in air. Formed by exogenous processes, it is widespread in peat bogs and in sedimentary iron ore deposits that are rich in phosphorus. The mineral is used as a phosphorus fertilizer and in making dark blue paint.