IOLITE
Iolite, also known as water sapphire, is a transparent, violet-blue, light blue, or yellow-grey mineral found in Sri Lanka, India, Madagascar and Burma. Iolite is different colours in different directions in the crystal. A cube cut from iolite will look a violet blue almost like sapphire from one side, clear as water from the other, and a honey yellow from the top. The name Iolite comes from the Greek word "Ios" meaning violet. Iolite was the secret weapon of the seafaring Vikings as they used slithers of Iolite in the first polarising filter. Using an Iolite lens they could determine the direction of the sun and therefore the direction of travel. It is mined in India, Sri Lanka, Mozambique, Zimbabwe, and Brazil. The Vikings probably mined Iolite from deposits in Norway and Greenland.
Hardness 7