Ferrous diferrifluoride, FeFe₂F₈

Ferrous diferrifluoride, FeFe₂F₈.10H₂O, or FeF₂.2FeF₃.10H₂O, obtained by the action of hydrogen fluoride on iron in the presence of nitric acid, crystallises in colourless octahedra, which appear flesh-coloured in thick layers. It gives the ordinary ferrous and ferric reactions only after addition of an acid.