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

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Iolite displays different colors when viewed in different directions.

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Iolite is usually faceted to highlight its transparency.

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Fine color

Iolite’s finest blue color can rival tanzanite’s vivid hue.

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Iolite’s pleochroism can be a challenge for cutters.

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Iolite is not treated for color enhancement.

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The mineral cordierite is known as iolite in the jewelry industry.

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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.

Iolite Description

Iolite History and Lore

Birthstones & Anniversaries

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


Iolite’s name is from the Greek word ios, meaning violet.


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.


  • 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


There are a number of processes used to alter the color, apparent clarity, or improve the durability of gems.

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Some gemstones have synthetic counterparts that have essentially the same chemical, physical, and optical properties, but are grown by man in a laboratory.

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Any gem can be imitated—sometimes by manmade materials or by natural materials chosen by man to impersonate a particular gem.

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gem love

Why We Love This Gemstone

Stunning Color

In its best colors, iolite can rival the beauty of tanzanite but at a fraction of the cost.


Usually transparent, iolite sometimes contains inclusions that cause attractive phenomena.


Iolite’s beautiful violet-to-blue hue is due to the presence of iron in its structure.

Quality Factors

The following factors combine to determine an iolite’s value.


quality factors

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


quality factors

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


quality factors

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

Carat Weight

quality factors

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

Iolite Quality Factors: The Comprehensive Guide


Explore sources, gemological research, and the role of gems in history.

Sri Lanka: The Gem Island

Peter C. Zwaan , Jun 1, 1982 Read Article

A Prospectors’ Guide Map to the Gem Deposits of Sri Lanka

C. B. Dissanayake and M. S. Rupasinghe , Sep 1, 1993 Read Article