Iolite : Is also known as the Gem of the Vikings. This is because they used thin slices of it as the first polarizing filter to determine the exact position of the sun. This way they could navigate themselves successfully in the ocean. The name comes from the Greek word Ion, meaning violet, because of it's color. The pleochroism, which helped the Vikings, means that the stone can be a purplish blue color when looked at in one direction, and a colorless to yellow color in another. It is found in India, Sri Lanka, Mozambique, Zimbabwe, and Brazil. There are also deposits in Norway and Greenland. It is the stone for the 21st Wedding Anniversary.