Chemistry: (Mg, Fe2) Al4Si5O18
Refractive index: 1.522 - 1.578
Hardness: 7 - 7.5
Specific gravity: 2.53 - 2.78
Cleavage: Distinct 1 direction
Heat sensitive: No
Wearability: Very Good
Special care instructions: None
The name iolite comes from ios, the Greek word for violet.
Like sapphire and tanzanite, its fellow blue gemstones, iolite is pleochroic- meaning it transmits light differently when viewed from different directions.
The Vikings made iolite's pleochroism a virtue by using thin slices of the stone as a light polarizer to navigate their trips.
By observing the sky through iolites, the Viking navigators were able to locate the exact position of the sun on overcast days.
Iolite does what a Polaroid does- it cancels out haze, mist, and clouds to make things appear clearer.
In fact, the stone has been called the "Viking's Compass."
Only officially named in 1912, iolite has been used and admired for centuries.
It was prevalent in jewelry in the 18th Century in Europe but today it is used somewhat infrequently.It is one of the few relatively available and affordable blue stone options, is rapidly gaining in popularity.
Arguably the gain is due more to exposure in mail-order catalogs and on cable shopping channels than to promotion by traditional jewelry stores.
It often has a steely, inky, or washed out blue color, but the best specimens can rival AAA tanzanite in the saturation of their blue-violet hue.
Iolite is frequently step cut to enhance color and often windowed and/or shallow cut to lighten the tone.
The cutter must orient the rough carefully, taking iolite's trichroism of blue, gray, and near colorless into account.
So far, no treatments have been successfully used to lighten the color or to remove inclusions, so one can assume that these gems are untreated.
Its hardness of 7-7.5 makes it a suitable jewelry use, though the cleavage must be taken into account.
Most of the iolite in world commerce comes from India, but substantial amounts are also mined in Tanzania, Brazil, and Sri Lanka.