Fine Iolite is Rare

We recently found some very fine pieces of iolite, not something that happens very often. That's because it's rare to find iolite in sizes weighing over 1 carat and with good clarity. High quality iolite is a strikingly beautiful stone when cut well so we wanted to know more about this unusual gem.

Many of the lesser-known colored gems are unheard of because they are relatively soft. This is true of gem varieties like fluorite, apatite, sphene and diopside. But iolite is actually quite a hard stone, with a rating of 7 to 7.5 on the Mohs scale, making it as hard as tourmaline and harder than tanzanite, peridot and all the quartz varieties. Iolite is not well known, simply because it is so difficult to find. If iolite was commonly available in gemstones of larger sizes, it might be as popular (and as valuable) as tanzanite.

Fine iolite is typically a soft violet-blue color with unusual pleochroic properties, meaning that it displays different colors when viewed from different angles. Iolite displays both light-blue and yellow-gray hues, in addition to its dominant violet-blue color. Gem cutters must be careful to orient the material correctly so that it appears violet-blue when viewed through the table (the top) of the stone.

Iolite's pleochroic properties were known to mariners who found practical applications for it. The Vikings reportedly used iolite as a polarizing lens, through which the exact location of the sun could be determined on overcast days, to aid navigation.

Iolite is composed of complex magnesium aluminum silicate with traces of ferric/ferrous iron and manganese. The magnesium is partially replaced by ferrous iron and manganese and the aluminum is partially replaced by ferric iron. Iolite is also known by the mineral name cordierite, after Pierre Louis Cordier, the French mineralogist who first described it in 1809. The name iolite comes from the Greek ios meaning 'violet'.

The value of iolite depends on the violet-blue color. The richer the blue, the high the value. Iolite is always untreated; in fact there are no known treatments to enhance the color or clarity of iolite.

Iolite deposits are found in India, Brazil, Canada, Germany, Finland, Madagascar, Mozambique, Burma, Norway, Sri Lanka, Tanzania, the USA and Zimbabwe. Most of the fine material we have been seeing recently comes from mines in Madagascar.