Iolite. A silicate of alumina, iron and magnesia, having a bright blue color and a vitreous or glassy luster. It is remarkable for its dichroism, and is also called dichroite.

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“Finally, brothers, whatever is true, whatever is noble, whatever is right, whatever is pure, whatever is lovely, whatever is admirable – if anything is excellent or praiseworthy – think about such things.”
– Philippians 4:8