water sapphire

from WordNet (r) 3.0 (2006)

water sapphire
    n 1: a deep blue cordierite often used as a gemstone

from The Collaborative International Dictionary of English v.0.48

Water sapphire \Wa"ter sap"phire\ [Equiv. to F. saphir d'eau.]
   (Min.)
   A deep blue variety of iolite, sometimes used as a gem; --
   called also {saphir d'eau}.
   [1913 Webster]