Iolite: Properties, Facts and Photos

What is Iolite?

Iolite, which is the gemstone variety of the mineral cordierite, is translucent to transparent with a blue to bluish-violet colour.

The colour of iolite is often compared to sapphire , but usually has more of a purple tint.

One of its most notable characteristics is pleochroism. Pleochroism is an optical phenomenon that enables a rock, mineral or gemstone to exhibit different colours when viewed from different angles.

Iolite was once known as dichroite, meaning "two-coloured rock."

Although many gemstones are pleochroic, most show so little colour change that it's almost unnoticeable. Cordierite and tanzanite both exhibit pleochroism with colour changes that are often easy to see.

Depending on the gemstone’s colour, the type of light, and the angle from which it’s viewed, iolite can look violet, blue, bluish-grey, green, yellow, or even colourless.

The finest-grade gemstones can easily be mistaken for blue sapphire or tanzanite. However, iolite is more readily available, making it far more affordable.

Iolite has never been widely marketed and therefore remains relatively unknown. This may well be because of its tendency to break. Although it grades 7 to 7.5 on the Mohs scale of mineral hardness, which makes it quite hard, it's not particularly tough. Hardness and toughness in rocks and minerals are not the same.

Hardness refers to the ability of one mineral to scratch another, while toughness, also known as tenacity, refers to a mineral's resistance to cracking, chipping, pressure or breaking. 

Iolite has a perfect cleavage in one direction, which means it can break easily as a result of a knock, pressure or even an extreme change in temperature. This makes cutting and polishing quite difficult.

Although its colour can vary, iolite is best known as a blue to bluish-violet coloured gemstone. Unlike tanzanite and blue sapphire, which are routinely heated, the colour of iolite is almost always natural.

Heat can interfere with a stone's chemical composition, which can enhance or change the colour completely.

Iolite History and Occurrence

The mineral cordierite was named after French geologist Pierre Louis Antoine Cordier, who first described it in 1809.

The gemstone iolite was officially classified and named in 1813. It's widely believed to have been known and used in Sri Lanka long before then.

The name comes from the Greek word 'ios', meaning violet.  

Iolite can be found in several countries around the world, including India, Brazil, Sri Lanka, Mozambique, Zimbabwe, Madagascar and Myanmar. It's believed to have been mined by the Vikings in Norway and Greenland.

In 1996, an iolite deposit was discovered in Wyoming in the USA. Further discoveries were made in 2004 and 2005.