fergusonite

from WordNet (r) 3.0 (2006)

fergusonite
    n 1: a dark mineral consisting of oxides of yttrium and erbium
         and tantalum and other minerals

from The Collaborative International Dictionary of English v.0.48

Fergusonite \Fer"gu*son*ite\, n. (Min.)
   A mineral of a brownish black color, essentially a
   tantalo-niobate of yttrium, erbium, and cerium; -- so called
   after Robert Ferguson.
   [1913 Webster]