Iolite is a precious gemstone form of cordierite, named after the French geologist Pierre Louis Cordier in 1813. It is a blue to violet colour, similar to Sapphire or Tanzanite. With a hardness of 7 to 7.5, it is softer than sapphire, but harder than tanzanite.
Its name comes from the Greek words Ios, meaning “violet”, and lithos, meaning “stone”. It exhibits pleochroism, a characteristic whereby it is one colour from the top, and another colour from the side. Seen from above it is purple, and it is colourless or very light brown from the side.
In ancient times Vikings used thin slices of iolite as polarizing filters, allowing them to determine the position of the sun, and therefore navigate with accuracy, in any weather. This lead it to be called “The compass of the Vikings”.
Most of the Iolite available today comes from Sri Lanka, Burma, India, Madagascar and Brazil. The world’s largest iolite crystal weighs over 24,000 carats, and was found in Wyoming, USA.