VIVIANITE  , a

mineral consisting of hydrated iron phosphate Fe3(PO4)2+8H20, 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 = z ~, 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 . Crystals were first found in Cornwall (at Wheal Jane, near Truro, associated with pyrrhotite) by J . G . Vivian, after whom the species was named by A . G . Werner in 1817 . The mineral had, however, been earlier known as a blue powdery substance, called " blue iron-earth," met with in peat-bogs, in bog iron-ore, or with fossil bones and shells . (L . J .