Stone Information & Mining

When tanzanite was first discovered, gemologists initially suspected it might be cordierite, a transparent, pleochroic, violet-blue gemstone known for thousands of years. Today, cordierite (named after geologist Pierre Cordier) is better known by its trade name, iolite, which comes from the Greek word "ios," meaning "violet."

Iolite's strong pleochroism makes the gem tricky to cut for the best color. This in turn continues to pose challenges to producers and buyers interested in promoting the attractive yet problematic gemstone to retailers as an affordable blue gem alternative.

This silicate of aluminum, iron, and magnesium has two distinctive features—a beautiful, violetish blue through slightly violetish blue hue derived from iron and a striking, eye-visible pleochroism. Its pleochroic colors differ with its bodycolor. Iolites that appear violet display light violet, dark violet, and yellow-brown pleochroic colors. Bluish iolites display colorless to yellow, blue-gray, and dark violet pleochroic colors. From some angles, then, a bluish iolite can actually appear completely colorless or yellow, and a violetish iolite can look brown.

Iolites are usually cut as faceted gemstones, but they are also frequently cut into cabochons.

Because iolite is fairly hard, it's often found in alluvial deposits. In addition to the gem gravels of Sri Lanka, iolite occurs in several areas of Africa, including Kenya and central Tanzania. Other iolite source countries include India, Brazil, and Norway. A significant iolite deposit was discovered in Madagascar in 1994.

Legend & Lore

According to legend, iolite is called the Viking Compass Stone. It's said that thin slices of iolite served as glare-reducers and polarizing filters that helped ancient Viking navigators locate the sun on cloudy days. This allowed the Nordic mariners to pinpoint their own location on the seas.

Whether or not the tales are true, iolite (mineralogists call it cordierite) can be fashioned into beautiful gemstones. 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.

The name iolite comes from the Greek word "ios," meaning "violet." Some believe that the gemstone aids sleep and helps to unlock creativity. Iolite is often cited as the twenty-first wedding anniversary gemstone.

Color

Iolite possesses two distinctive features—a beautiful, violetish blue through slightly violetish blue hue derived from iron and a striking, eye-visible pleochroism. Its pleochroic colors differ with its bodycolor. Iolites that appear violet display light violet, dark violet, and yellow-brown pleochroic colors. Bluish iolites display colorless to yellow, blue-gray, and dark violet pleochroic colors. From some angles, then, a bluish iolite can actually appear completely colorless or yellow, and a violetish iolite can look brown. Some gemstones can look grayish or nearly colorless.

Cleaning

It's important to avoid steam or ultrasound for cleaning iolite: Warm, soapy water works best.

This information was excerpted from the GIA's Gem Encyclopedia with permission from the GIA