• Name comes from Greek ios meaning violet.
  • The Vikings used thin pieces of iolite as navigational aids. Like Polaroid sunglass lenses, the gem slices eliminated haze and glare. By looking through one, it was possible to determine the sun’s position and to sail on overcast days.
  • Gem for the 21st wedding anniversary.



  • Color: Light to dark blue and violet. Typically soft and subdued, but can approach the richness of tanzanite and blue sapphire.
  • Clarity: Often lightly included. Minor clarity characteristics are accepted.
  • Cut: Usually faceted in traditional shapes and styles. Sometimes cabochon cut.
  • Carat Weight: Normally available in sizes up to about 10 carats.



  • Iolite is one of the gems for which there are no established treatments.



  • Classified as a mineral species, and known to mineralogists as cordierite. Composed primarily of magnesium, aluminum, silicon, and oxygen; chemical formula Mg2­A14Ai5O18. Color caused by trace amounts of iron.
  • Often displays strong pleochroism – from some angles appearing blue or violet, and from others grayish, yellowish, or almost colorless. (If the gem is loose or in an open setting, hold it up to a bright light and look through the top; then through the sides and ends.) Because of this property, iolite must be carefully oriented to show its best color when cut.
  • Once called “water sapphire” because of the strong contrast between the deep blue face-up color and the weaker ones seen from other directions. The term is now considered a misnomer.



Iolite needs gentle wear and care. Protective setting recommended.

  • Hardness: Moderate scratch resistance. Rates 7 to 7.5 on the Mohs Hardness Scale.
  • Toughness: Fair resistance to chipping and breaking because of cleavage (a tendency to split in certain directions due to crystal structure patterns).
  • Stability: No routine concerns for gem owners.
  • Cleaning: Liquid cleaner, or detergent and water. NEVER USE ULTRASONIC.