Iolite
Iolite (ī"o*līt) , noun
[Greek 'i`on a violet + -lite.]
(Mineralogy) 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.