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vivianite Mineral, Fe3(PO4)2.8H2O; sp. gr. 2.9; hardness 1.5–2.0; monoclinic; greyish-blue, occasionally colourless; vitreous lustre; crystals prismatic, rod-like, acicular, and stellate masses; cleavage, one, perfect, pinacoidal; occurs in phosphorus-rich, sedimentary iron ores and peat bogs, in association with siderite, in a reducing environment with organic remains present, and in close association with fossil bones and shells. It is used as a cheap blue pigment.