It is hard to understand why zircon is not more popular with jewelry makers. Its hardness and fracture are no worse than in gemstones such as garnet or tourmaline but has added qualities of a consistant adamantine lustre, strong double refraction, attractive colours and affordability. The likely reason is its closeness to the artifical gemstones, Zirconia and the public believing that somehow the two are related and Zircon’s are in fact no natural crystal but rather they are man made. They could really do with a public relations makeover, and a new name!
Zircon is a brilliant transparent stone that comes in a number of natural colours: yellow, brown, orange, violet, green, blue and red. The most common are grey-brown to red-brown, while the most popular is golden brown. Colourless zircon is quite rare and when cut as a gemstone could easily be confused with diamond, because of its strong brilliance and fire. Like diamond, zircon has an adamantine lustre. Zircons can be heat treated to change and bring out color.
types of zircon
- Zircon contains traces of uranium and thorium, both of which are radioactive, and as a result can differ in mess, specific gravity, refractive index and colour. There are two distinct types of zircon. High zircon is yellow-brown and the harder, more desirable stone. Low (decayed) zircon is greenish yellow to greenish brown, and is softer as a result of radioactive deterioration.
- Zircon has medium to distinct differences in colour when observed from different directions. The strength of this dichroism depends on the type of zircon and the intensity of colour; high zircon with a dark colour will produce the strongest dichroistic effect. Another feature of zircon is its uneven colour distribution, which can be useful in identifying the stone.
Treatments and Imitations
- Zircon has been heat treated for hundreds of years. This is an accepted practice that can change the colour of zircon to red. blue, orange or green, but some colours are not stable and will revert back or fade. Because of the scarcity of natural colourless zircon, reddish brown ones are heated to make them colourless; with prolonged exposure to sunlight or UV radiation, however, they can become dark brown again. Brown material can also be heated to a vibrant blue colour, and if the colour fades the stone can be reheated to regain its colour. Alternatively, reheating blue stones in the presence of oxygen will turn them golden yellow.
- Zircon is sometimes imitated with colourless glass and synthetic spinel. Green and yellow varieties of zircon could be confused with sapphire, demantoid garnet, chrysoberyl, hessonite garnet, topaz or tourmaline. Zircon has been used in place of diamonds in some antique jewelry. Look at the stones through a loupe to spot the scratches and scuffs on the facet surfaces and chips on the facet edges; this will distinguish them from diamonds.
Working with zircon
- Unfortunately, heat treatment affects the properties of zircon, making a stone more susceptible to wear and tear. A heat-treated gemstone will not only wear down more quickly over time, but also become more fragile at the junctions of the faceted surfaces.
- Zircon has a conchoidal fracture, which makes it a naturally brittle material. Despite being moderately hard, it will chip if knocked, so care needs to be taken during setting and polishing. Zircon is better used for pendants and earrings; if you are contemplating using it as a ring stone try to use an unheated stone and design a protective setting.
- Zircon possesses strong double refraction, which means that you will see a doubling of the back facets when you look into the stone through the table. The zircon cut was designed to show off this special property. This cut is a development of the brilliant cut that maximizes the light entering and leaving the gemstone, to display the full dramatic impact of double refraction.