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Colour: Various colours
Found in: Mostly Thailand, Sri Lanka, Myanmar, Australia. Also USA, Russia, Korea, Germany, Brazil, France, Canada, Norway, Tanzania.
Mohs Hardness: 7.5
Refractive Index: 1.81-2.02
Formula: ZrSiO4 |
Commonly mistaken for cubic zirconia, zircon is the birthstone of December. In the Middle Ages, it was believed zircon would fend off evil spirits and promote good sleep.
The gemstone became a prominent feature in jewellery during the Victorian era and was a particular favourite of Tiffany and Co.’s head gemmologist, George Kunz.
As a fan of zircon’s captivating dispersion, he suggested the gemstone be named ‘starlite’, though it was never picked up by the trade.
Given the name similarity, most people confuse cubic zirconia - a synthetic gem with no natural counterpart - with zircon, a completely different natural mineral with no commercial production of synthetics.
This misconception is further fuelled by the fact that both have been used as imitations of diamonds.
Zircon was chosen as a diamond imitation given its sub-adamantine lustre which is close to diamond, as well as its strong brilliance, dispersion, and high refractive indices.
The downfall is its brittleness, meaning the stone is chipped somewhat easily, particularly when parceled together. A gemmologist can easily distinguish diamond from zircon by the doubling of the back facets exhibited by the latter.
Perhaps one of the most well-known facts about zircon is that it is the oldest mineral on the planet.
A zircon crystal found in Jack Hills, Western Australia, has been dated at nearly 4.4 billion years old – 160 million years younger than the age of Earth itself. The crystal is likely a remnant of the planet’s oldest continental crust.
This dating of zircon is possible given traces of radioactive elements, such as thorium and uranium, existing within the crystal lattice. These elements decay over a known amount of time, allowing geochronologists to measure the amount of decay and thereby estimate their age.
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| Above: Rough Zircon - Gemstones.com; Polished Zircon – Doug Menadue |
This radioactivity also results in the gradual deterioration of the crystal lattice with time.
Zircons start as what’s referred to as ‘high type’ – red, brownish orange, yellow, treated blue and colourless gemstones that are doubly refractive, crystallizing in the tetragonal system.
With time, the radioactive trace elements decay the crystal structure, turning them into ‘low type’ zircons – usually green in colour with an amorphous structure. These low-type zircons are also termed ‘metamict’.
Intermediate zircons also exist, with the level of decay sitting between the unaltered high type and the amorphous low type.
Not to worry though – the radiation levels are extremely low as trace elements and are generally completely safe to wear.
Though natural zircon is sufficiently abundant to not warrant the commercial availability of synthetic zircon, treatments are common to achieve various colours.
The fantastic and striking, blue-coloured zircons are the result of heating what was originally reddish-brown material from southeast Asia or Australia at around 1000C.
Whites, yellows, and greens can also be produced through various heat-treating conditions.
It is important to note the colourless, yellow, red, and blue zircons achieved through treatment cannot be distinguished from the naturally coloured material and so disclosure cannot be accurately given.
Considering its brilliance, strong fire, and alluring colours particularly blue, zircon seems to be underappreciated by jewellery consumers. The silver- lining being is, of course, that these impressive gemstones can bring a jewellery piece to life with even the most modest of budgets.
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