The Collaborative International Dictionary of English v.0.48:

Vivianite \Viv"i*an*ite\, n. [So called by Werner after the
   English mineralogist F. G. Vivian.] (Min.)
   A hydrous phosphate of iron of a blue to green color, growing
   darker on exposure. It occurs in monoclinic crystals, also
   fibrous, massive, and earthy.
   [1913 Webster]