Distinguishing Features
Zircon found in Australia is the oldest mineral on earth: 4.4 billion years old.
Some Zircons irradiate themselves and change properties with the uranium contained. Gemologists classify zircons into high, intermediate and low types, depending on their properties directly related to the degree of radiation.
The Most Desirable Picks
Virtually all the zircon used in jewellery is high, fully crystalline.
Colour: Colorless zircon is known for its brilliance and fire. These zircon properties are close enough to the properties of diamonds to account for centuries of confusion and give rise to a role as a diamond alternative. Blue remains the dominant colour of zircon in consumer preference. Warm hues such as yellowish and reddish-brown have gained people’s fondness for autumnal russet and earth colours. Red and green zircons play their role as collector stones. Many other colours of zircon await designers and consumers.
Clarity: Zircons are relatively free of inclusions, but many untreated zircons have a cloudy or smoky appearance. This smokiness made zircon a popular gem for mourning jewellery in Victorian times.
Cut: Brilliant style usually shows the best luster and fire of zircon. Step cuts and combination cuts are available in the market to choose from.
Carat Weight: Typical sizes depend on colour. Blue or green stones normally range from 1 carat to 10 carats and yellows and oranges up to around 5 carats. Reds and purples are usually smaller.
Origins
Zircon sources often overlap with sapphire sources, such as Madagascar, Sri Lanka, Myanmar, Vietnam, Cambodia and Australia.
Cambodia is the primary source of heat-treatable zircon, its neighbour country Thailand is the cutting centre and a wholesaler to the world.
Significant Pieces
This gem was thought to induce sound sleep, drive away evil spirits, and promote riches, honor, and wisdom in the Middle Ages. Blue zircon was a particular favourite in Victorian times, when fine gems were often featured in English estate jewellery dating from the 1880s.
Formation
Zircon crystals grow in a wide variety of different rock types. They can show a wide range of refractive index, specific gravity, and double refraction properties.
Zircons irradiate themselves and change properties with the uranium or thorium contained. However, this metamict process is reversible with heat treatment.