The Collaborative International Dictionary of English v.0.48:

Samarskite \Sa*mar"skite\, a. [After Samarski, a Russian.]
   (Min.)
   A rare mineral having a velvet-black color and submetallic
   luster. It is a niobate of uranium, iron, and the yttrium and
   cerium metals.
   [1913 Webster]

WordNet (r) 3.0 (2006):

samarskite
    n 1: a complex black mineral occurring in pegmatites