Zircon

History

Zircon is a natural gemstone that has been valued for its beauty since ancient times. It is one of the oldest minerals on Earth, with some pieces dating back over 4 billion years. In the Middle Ages, zircon was thought to promote sleep, bring prosperity, and bestow honour and wisdom to its wearer. Despite its long history, zircon remains an underrated gemstone often confused with its synthetic counterpart, cubic zirconia. The name zircon comes from the Persian word "zargun," meaning "gold-hued". Zircon is a December birthstone, which has increased its popularity in modern times.

Mineral Origins

Zircon is found worldwide, particularly in igneous rocks and alluvial deposits. Southeast Asia is a primary source for gem-quality zircons, with notable deposits in Cambodia, Sri Lanka, Vietnam, and Thailand. Sri Lanka produces a variety of colours, including rare cat’s-eye zircons. Cambodia is a chief source of material that can be heat-treated to become colourless or blue. Myanmar is known for yellowish and greenish stones found in gem gravels. While gem-quality crystals are rare, zircon is also found in other locations such as Australia, Canada, France, Tanzania, and the United States. Zircon forms with a chemical formula of ZrSiO4 + Fe, U, Th, Hf.

The 4 C’s

When assessing zircon quality, several factors play a crucial role. These include the 4 Cs: colour, clarity, carat weight, and cut.

Colour

Zircons come in a wide array of colours, including earth tones like cinnamon, sherry, yellow, orange, and red. Blue is the most popular and expensive colour, although most blue zircons are heat-treated. Green is another sought-after colour, with bright green being extremely rare and prized by collectors. Other colours include purple, which obtains its colour from natural radiation, and various shades of red such as rose, champagne and cognac. Yellow zircon is sometimes called "melichrysos", and pale yellows have the trade names "jargoon" or "jargon". Reddish brown zircon is known as "hyacinth" or "jacinth". Colourless zircons are called "Matara" after the Sri Lankan city where they are mined.

Clarity

Zircons are generally relatively free of inclusions. Untreated zircons can sometimes appear cloudy or smoky due to metamictization. This smokiness is generally undesirable, except in some green zircons. Most zircons used in jewellery are eye-clean. Metamict zircons, which have undergone structural damage due to radiation, may have a hazy or smoky appearance. Inclusions that cause a cat's-eye effect are rare.

Carat

The size of zircon gemstones varies depending on the colour. Red and purple stones tend to be small, while yellow and orange gems can be found up to five carats. Blue and green zircons commonly range from one to ten carats. Larger sizes are also available, but are less common. Zircons tend to weigh more than other gems of similar size.

Cut

Zircon is commonly cut in brilliant styles to showcase its luster and fire. The "zircon cut," a modification of the brilliant cut with extra facets, was used historically. Other cuts include step cuts and mixed cuts. Due to zircon's brittle nature, cutting can be a challenge for lapidaries. They must account for its birefringence and pleochroism. Facets may appear doubled or fuzzy when viewed through the table.

Be Aware of

Enhancements

Most zircons, especially blue and colourless ones, undergo heat treatment to enhance their colour and clarity. This process is stable and does not require additional care. Heat treatment can cause metamict gems to recrystallize, which improves their clarity. Heating can also produce red and golden colours and can lighten or remove smokiness from green zircons. At lower temperatures heating produces red and golden colours. Colourless, blue and golden brown stones may only show one fine line at 6535 and also a weaker line at 6590 in the absorption spectrum.

Simulants

Zircon has been used as a diamond simulant due to its high refractive index and dispersion. Colourless zircons, when properly cut, can be convincing diamond imitations and may even outshine mediocre diamonds. However, diamonds are much harder than zircons. Zircons also have a very brittle tenacity, which means their facet edges are prone to chipping. Zircons have strong birefringence which can cause a fuzzy appearance if not correctly oriented when cut. Zircon has also been sold under misleading names such as "Matara diamonds," "Ceylon diamonds," and "Siam aquamarines," which is unethical.

Synthetics

While synthetic zircons have been created for research, there is no known jewellery use for them. Cubic zirconia, often confused with zircon, is a lab-created material with a different chemical composition and crystal structure.

Final Thoughts

Buying Tips

When buying zircon, seek out retailers who specialize in gems to ensure you are getting a genuine and high-quality stone. Because of their value and beauty, zircon is a popular stone for collectors. Be aware that much of the material sold as "natural purple zircon" is in fact cubic zirconia. Always verify the information on a gem report to ensure it is authentic.

Jewellery Care

Zircon is a relatively hard but brittle gemstone. Store zircon jewellery carefully to prevent facet edges from chipping. Protective settings are recommended for rings. Zircon jewellery should be reserved for occasional wear. Clean zircon using warm soapy water and a soft brush. Ultrasonic and steam cleaners are not recommended. Some heat-treated zircons can revert to their original colours if exposed to bright light for too long.