Iolite

July 23, 2020

Iolite is a uniquely coloured, affordable and abundant mineral and yet it is still one of the lesser known and underappreciated gems. Iolite is known as the stone of of leadership, confidence and inner strength and is known as the Viking’s compass. According to Norse legend Vikings were said to have used slices of iolite as a polarizing filter which they held up to the sky to help locate the sun on a cloudy day out at sea.

Iolite is the trade name given to the blue/violet variety of cordierite, a magnesium, aluminium silicate mineral. Fine iolite can display a deep blue-violet through to a pale blue-violet colour with some more vivid stones challenging the likes of tanzanite. This colour, derived from iron, is naturally occurring and cannot be enhanced by man unlike other blue hued rivals from inexpensive blue topaz through to the finest blue sapphires where treatments are often essential to alter colour and clarity to a more desirable and saleable level. The lack of consistency with iolite’s colour and with no current treatments available to correct it is possibly a contributing factor to its lack of popularity within the industry. 

Unearthed in metamorphic and igneous rocks, iolite can be found in various locations around the world, Sir Lanka, India, Tanzania and Australia being the most prominent. With a hardness of 7-7.5 on MOH scale it is suitable for rings as well as other forms of jewellery and is often an affordable substitute for tanzanite and sapphire when rich colour and clarity are present. Although eye-clean stones can be found, they are becoming harder to find in larger carat sizes, so it’s typical to find eye-visible healed fractures in stones over 5 carats. Quite often stones will contain numerous metallic, plate-like inclusions of hermatite exhibit iridescence and, on occasion, many present a glittering aventurescence reminiscent of sunstone (a gorgeous red-orange glittery variety of feldspar). 

As delicious as this sheen may be it is iolite’s striking, eye visible pleochroism that really gets my heart fluttering. Pleochroism refers to a crystal’s ability to display different colours depending on the crystals axis it is viewed from. This optical phenomenon results in ‘differential selective absorption’ (where wavelengths of white light are absorbed differently due to a crystal’s internal chemical structure). Iolite is an orthorhombic crystal and displays trichroism, meaning it displays three different colours from three different crystal axis. A stone that displays two different colours would be described as ‘dichroic’ (eg: sapphire). These pleochroic colours differ depending on the body colour of the stone. Iolite that appears violet shows light violet, dark violet, and yellow-brown. More bluish toned iolites show colourless to yellow, blue-grey, and dark violet. Not only is this magical display of light an important method of identifying iolite but also a fun-fact to share.

The name iolite originates from the Greek word “ios” meaning violet. Other names such as ‘water sapphire’ and ‘dichroite’ have been used in the past, both in reflection to iolites pleochroic properties. ‘Water sapphire’, one that seems to have stuck, can be a misnomer that suggest iolite is a different mineral altogether. It actually refers to stones appearing sapphire-blue from one angle to water-clear from another. This particular quirk poses a challenge from gem cutters who need to ensure the strongest wavelength of light is visible through the talbe facet.

Bunny Bedi, owner and designer at Made In Earth, has also found the fickle flow of iolite both a positive and negative. “Although iolite is an abundant mineral, high quality stone suitable for faceting have become difficult to obtain for a fair price. In the meantime, we’ve embraced the uniquely included rough that show aventurescence and cut them into cabochons. Luckily, we currently have exquisite stones in calibrated sizes with excellent clarity, but larger faceted stones over 10mm tend to have surface reaching fractures and lack the brilliance of our smaller stones.” 

Despite its fabulousness, iolite is still an unfamiliar gemstone to most, overlooked because of unreliable and inconsistent availability in the market. It’s always good to embrace what you have to work with and iolite is no strange to unique inclusions and party tricks.

 


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