The Collaborative International Dictionary of English v.0.48:

Amethystine \Am`e*thys"tine\, a. [L. amethystinus, Gr. ?.]
   1. Resembling amethyst, especially in color; bluish violet.
      [1913 Webster]

   2. Composed of, or containing, amethyst.
      [1913 Webster]

WordNet (r) 3.0 (2006):

amethystine
    adj 1: containing or resembling amethyst

Moby Thesaurus II by Grady Ward, 1.0:

22 Moby Thesaurus words for "amethystine":
   lavender, lilac, livid, magenta, mauve, mulberry, orchid,
   pansy-purple, plum-colored, plum-purple, purple, purplescent,
   purplish, purply, purpurate, purpure, purpureal, purpurean,
   purpureous, raisin-colored, violaceous, violet