Iolite According to legend, Vikings used iolite slices to reduce glare when checking the sun’s position.

ABOUT IOLITE

In legends, ancient Viking navigators used thin slices of iolite as filters to help locate the sun on cloudy days. Whether or not the tales are true, iolite (mineralogists call it cordierite) can be fashioned into beautiful gems. Strongly pleochroic iolite has been incorrectly called “water sapphire,” as it can display a blue to violet hue in one direction and pale yellow to colorless in another.

BIRTHSTONES & ANNIVERSARIES

Iolite is the gemstone for the twenty-first wedding anniversary.

QUALITY FACTORS

The following factors combine to determine an value.

COLOR

Iolite’s most desirable colors are in the violetish blue to fine blue range.

CLARITY

Properly oriented inclusions can cause cat’s-eyes and aventuresence.

CUT

Iolite is most often faceted, as this cutting style serves to highlight its fine transparency.

CARAT WEIGHT

Fine-quality faceted iolites over five carats are relatively rare in the market.

IOS

Name is from the Greek word ios, meaning violet.

PLEOCHROIC

When you turn iolite, you’ll see three distinct colors in three crystal directions.

AU NATURAL

Iolite is not typically treated. This is an attractive selling point for some consumers.

FACTS

• Mineral: Iolite (Cordierite)
  
• Chemical composition: Mg₂Al₄Si₅O₁₈
  
• Color: Violetish blue (pleochroic colorless-yellow)
  
• Refractive index: 1.542 – 1.551
  
• Birefringence: +0.045, -0.011
  
• Specific gravity: 2.61
  
• Mohs hardness: 7.0 – 7.5