The Collaborative International Dictionary of English v.0.48:

Garnierite \Gar"ni*er*ite\, n. [Named after the French geologist
   Garnier.] (Min.)
   An amorphous mineral of apple-green color; a hydrous silicate
   of nickel and magnesia. It is an important ore of nickel.
   [1913 Webster]

WordNet (r) 3.0 (2006):

garnierite
    n 1: a green mineral consisting of hydrated nickel magnesium
         silicate; a source of nickel