A Deep Dive On Zircon
Zircon is a naturally occurring mineral composed of zirconium silicate that dates back 4.4 billion years ago.
Because of its exceptional durability and resistance to heat, weathering, and chemical alteration, zircon is highly valued by geologists for studying the Earth's early history.
Tiny zircon crystals preserved in ancient rocks provide important evidence about the formation of the Earth's crust and the presence of water on the planet during its earliest stages.
Concentric layers inside crystals record distinct geological events that occurred over 100 million years ago!
The History Of Zircon
Zircon's name comes from the Persian word “zargun” which means gold-coloured. Others believe the word originates from the Arabic word zarkun which means vermillion or cinnabar.
Zircon has been in use in jewellery since ancient times while there is no recorded date when zircon was first discovered, it is believed to have been in use over 2000 years ago.
In 1789, Martin Klaproth analysed zircon & in doing so he discovered a new element inside of - which he named zirconium.
In the Middle Ages zircon was thought to drive away evil spirits & promote riches, honor & wisdom.
Lots of zircon can be found in estate Jewellery from the Victoria period.
In the early 1900s zircon was widely used as a diamond simulant. Toward the mid 1900s zircon was widely confused with cubic zirconia, for this reason it lost some of its popularity.
Zircon - December’s Birthstone
Zircon is one of three birthstones for the month of December as well as turquoise & tanzanite. While both turquoise & tanzanite (tanzanite can also have a strong violet colour) are largely blue in colour, zircon encompasses a variety of colours, giving people another choice if blue is not their go to colour.
Zircon Colour Varieties
Zircon comes in various colours such as blue, red, yellow, orange, brown & green.
The colour that forms is largely due to the impurities within the crystal lattice. Additionally, the geological conditions by varying temperature, pressure & surrounding minerals all contribute to the colour of zircon. Prolonged radiation can also cause zircon to turn green.
The colour of zircon largely determines its value. The rarity & desirability largely determine what the price will be with red & green hues & often commanding the highest prices.
Blue Zircon
Occasionally called starlite, blue zircon is a very popular variety & exhibits a good sparkle & often a vivid colour. Blue zircon may display a green or yellow overtone due to the gem's pleochroic properties.
Blue zircon is often put in comparison with sapphire but blue zircon often has the lighter tone of the two.
Most blue zircon available on the market is heated brown zircon. One of the top producing areas of blue zircon is from Cambodia’s Ratanakiri mines.
Blue zircon has the highest demand of all zircon colours, as such it drives up the value of these stones.
Colourless Zircon
Colourless zircon is often used as a diamond alternative with its excellent brilliance & clarity with flashes of multi-coloured light. It has a striking similarity that makes it an affordable alternative to diamond.
Colourless zircon is known as matara which is named after the city in Sri Lanka in which it is found. Historically, colourless zircon was often called Jargoon. Although jargoon could also refer to pale yellow or pale grey.
Brown zircon
Brown zircon is sometimes called Hyacinth. It is one of the most common forms of zircon & it is often heat treated to produce blue or colourless zircon.
Red Zircon
This relatively rare variety of zircon, sometimes called hyacinth, has been called so since ancient times, named after the blooming flower. Its rarity in finer qualities makes it an attractive option to collectors.
Pink Zircon
Associated with romance, passion & love pink zircons are a delicate expression of femininity.
Golden & Yellow Zircon
Appreciated for their warm sunny hues, unlike blue zircon, the yellow variety occurs naturally and undergoes no heat treatment. Gem quality yellow zircon with top colour saturation & clarity are rare in sizes above 5 carats and will command premiums.
Orange Zircon
Mashewa zircon are orange stones from Tanzania’s Mashewa mines.
Green Zircon
Sri Lanka is one of the world's leading producers of green zircon.
This colour variety of zircon develops naturally from prolonged exposure to internal radiation from trace elements uranium & thorium. This natural radiation creates a variety of shades of green. Regarded as the rarest variety of zircon, green stones are much rarer than the brown, yellow or blue varieties.
(Picture above shows a ring with a central Tsavorite garnet surrounded by multi coloured zircon stones)
The Green Dragon Zircon
The largest faceted green zircon in the world weighing 200 carats was discovered in Madagascar.
Unlike diamonds, sapphires & rubies, zircon has very few individually named zircons partly because they do not sell for millions at auction houses like Christies. Although exceptional zircons are associated with museum collections, like the Smithsonian blue zircons.
Quality Factors Of Zircon
As with any gemstone, its value is determined by the four Cs.
Colour
As discussed, reds & greens hold the highest value due to rarity. Deeply saturated stones with vivid colour & without being overly dark are the most sought after.
Clarity
Tiny inclusions such as pinpoints, needles or clouds or crystals can form inside the zircon impacting the clarity & consequently the value of the gemstone.
Zircon is classified as a type 1 gemstone, which means they are usually free of visible flaws; however, finding microscopic inclusions under magnification is totally normal.
Carat
Zircon of good gem quality over 10 carats is incredibly rare. Such stones will command premiums.
Cut
Zircon is often cut into the brilliant shape to maximise its fire. A well cut zircon can make it sparkle like a diamond increasing its value whereas a poorly cut zircon will appear dull meaning lower value.
Zircon Quality - High, Medium Or Low
Zircon is often classified into three categories, high, medium & low. These categories are directly determined by the amount of radiation-induced damage, which affects the stones properties.
High zircons have normal crystal structures & display normal physical & optical properties. Most zircon used in jewellery is high zircon.
Medium zircons have some structural damage and low zircons may have extreme structural damage.
The reason zircon experiences this radiation damage is because its crystal lattice naturally attracts elements like uranium & thorium. The way zircon undergoes this radiation is unique to zircon.
Once the radiation damage reaches a certain point it causes the zircon to transform into a glass like state known as a metamict state.
While zircon can be radioactive, it is important to know that levels are so low that they pose no threat to human health!!
Zircon Vs Cubic Zirconia
However, zircon should not be confused with cubic zirconia, which is a synthetic material created in laboratories to imitate diamonds. Unlike cubic zirconia, zircon is a natural gemstone with unique physical and chemical properties. CZ is a homocreate - which is a material that has no natural counterpart.
Both of these gemstones contain the elements zirconium & oxygen but their chemical formulas and crystal structures differ, as such they have different optical properties. While zircon & cubic zirconia may look similar by eye they can easily be distinguished by a quick lab analysis.
Zircon Vs Diamond
Zircon has many interesting characteristics such as high refractive index and dispersion, which has made it the natural choice for a diamond simulant.
When cut well zircon can outperform the visual effects of an average diamond however poor cuts can make these gems appear dull.
Zircon's relative softness means that they are likely to get scratched, unlike diamonds.
One major optical difference between zircon & diamond is birefringence. Diamonds have none yet zircons have extremely strong birefringence due to facet image doubling.
Although zircons are often used to simulate diamonds, selling them as diamonds is not ethical. Colourless zircons have been sold as Matara or Matura diamonds or Ceylon diamonds. While in local culture they are often referred to as Ceylon diamonds in Sri Lanka, this can be misleading to buyers.
Heat Treated Zircon
While zircon is a naturally occurring gemstone, heat treatment of zircon is a common practice in the industry to either alter the colour or enhance it.
While Zircon comes in many colours, almost all colourless & blue zircon has been heat treated. Typically, brown or reddish brown stones undergo heat treatments.
Some of the irradiation damage in medium & low zircons can be reversed by heat treatment.
Zircon’s Sources
The mineral is commonly found in igneous, metamorphic, and sedimentary rocks throughout the world. Zircons appear on every continent but gem quality ones are typically found in river bed deposits.
The largest sources of zircon in the world are Australia & South Africa.
Sri Lanka, Cambodia, Mozambique, Myanmar, China & Indonesia are also producing countries.
Colour Change Zircons
Colour change can exist in zircons. In different lightings some zircons can display different colours, for example green hues will change to blue hues.
Zircon Properties
Gem-quality zircon is prized for its brilliance, strong dispersion, and high refractive index, giving it a sparkling appearance that is often compared to diamonds.
Hardness
Zircon has a hardness between 6 - 7.5 on the MOHs scale of hardness.
Zircons, due to their brittle tenacity, require protective settings in jewellery. Additionally, zircon is best reserved for occasional wear.
Luminescence
Although not all zircons will show any luminescence some display an intense glow.
Birefringance
This optical property of zircon means, you can see twice as many facets & it has an intense double sparkle, giving the gem a unique doubled appearance.
How to care for zircon jewellery?
Due to their brittleness, never clean them with ultrasonic cleaners. Use mild soap, warm water & a soft brush instead.
It is always best to keep your zircon jewellery stored separately from other jewellery. Gems stored together can rub which may cause damage.