Legend has it that when the initial Viking mariners ventured deep into the Atlantic Ocean they used a secret gem compass that helped them in determining their position. This gemstone, as it was later found out, was the natural iolite gemstone. Ancient mariners considered it as the worlds first polarizing filter. By using thin pieces of iolite gem and looking through it, navigators could determine the exact position of the sun and thereby navigate their way safely to the New World and back.
Another ancient Greek name associated with the iolite gem is dichroite or two-colored rock. This name actually portrays the strong pleochroism quality that the gem has. Iolite was also known as water sapphire in the ancient days as a cube cut from natural iolite rough resembles a sapphire from one side - clear as water from the other end and honey yellow from the top. Closer to home in India, the gem is known as kakaneeli.
The chemical composition of iolite is magnesium aluminium silicate (Mg2 Al 4 Si5 O18). The specific gravity ranges from 2.57 to 2.66 and the refractive index range vary between 1.53-1.54 and 1.54-1.55. Iolites hardness on Mohs scale ranges between 7 and 7.5.
The most striking feature of iolite gemstones are the pleochroism property that it has. The property is caused by an optical phenomenon by which the grains of a stone appear to have different colors when observed at different angles. The iolite gemstone exhibits very strong pleochroism that can be seen with the naked eye. It shows yellow, light blue and dark violet-blue pleochroic colors when viewed from different angles. And therefore it leaves many people wondering what color is iolite.
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