a mineral consisting of hydrated iron phosphate Fe 3 (PO 4) 2 +8H 2 0, 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= 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. 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 ironearth," met with in peat-bogs, in bog iron-ore, or with fossil bones and shells. (L. J. S.)