The Collaborative International Dictionary of English v.0.48:

Gadolinite \Gad"o*lin*ite\, n. [Named after Gadolin, a Russian
   chemist.] (Min.)
   A mineral of a nearly black color and vitreous luster, and
   consisting principally of the silicates of yttrium, cerium,
   and iron.
   [1913 Webster]

WordNet (r) 3.0 (2006):

gadolinite
    n 1: a mineral that is a source of rare earths; consists of
         silicates of iron and beryllium and cerium and yttrium and
         erbium [syn: gadolinite, ytterbite]