Leonard James Spencer, 1911 Encyclopædia Britannica, Volume 28… (1911)
“ VIVIANITE, a mineral consisting of hydrated iron phosphate Fe3 (PO4) 2+8H2O, crystallizing in the monoclinic system. The crystals possess a perfect cleavage parallel to the plane of symmetry and are usually bladed in habit; they are soft (H=1/2) , flexible and sectile. The specific gravity is 2.6. When unaltered and containing no ferric oxide, the mineral is colourless, but on exposure to the light it very soon becomes of a characteristic indigo-blue colour. ”
