The Collaborative International Dictionary of English v.0.48:

Leucoxene \Leu*cox"ene\ (l[-u]*k[o^]ks"[=e]n), n. [Leuco- + Gr.
   xe`nos stranger.] (Min.)
   A nearly opaque white mineral, in part identical with
   titanite, observed in some igneous rocks as the result of the
   alteration of titanic iron.
   [1913 Webster] leukemia