What is "dichroite"

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.

n. (context mineral English) iolite.