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]WordNet (r) 3.0 (2006):
fergusonite n 1: a dark mineral consisting of oxides of yttrium and erbium and tantalum and other minerals