The Collaborative International Dictionary of English v.0.48:

Iolite \I"o*lite\ ([imac]"[-o]*l[imac]t), n. [Gr. 'i`on a violet
   + -lite.] (Min.)
   A silicate of alumina, iron, and magnesia, having a bright
   blue color and vitreous luster; cordierite. It is remarkable
   for its dichroism, and is also called dichroite. A variety
   called Caribbean iolite has a lighter blue color.
   [1913 Webster +PJC]

The Collaborative International Dictionary of English v.0.48:

Dichroite \Di"chro*ite\, n. [See Dichroism.] (Min.)
   Iolite; -- so called from its presenting two different colors
   when viewed in two different directions. See Iolite.
   [1913 Webster]