While blue zircon shares a similar name with the synthetic cubic zirconia, it's actually a very real gem. Not only does blue zircon occur in nature, it compares favorably to the more widespread blue topaz, offering a similar range of blue shades. However, the stones differ in key areas such as common cuts and the all-important price factor.
Color Comparison
Although zircon and topaz both occur as colorless gems in nature, both stones often undergo heat treatment to produce blue hues. While the intensity of zircon's particular blue shade ranges from a light pastel to a deep, vibrant hue, blue zircon of any intensity typically has a greenish tinge. Blue topaz comes in a wide range of blue shades and depths of saturation, but these shades lack a green tinge, favoring instead a pure blue tone.
Contrasting Composition
The chemical composition of gemstones can come into play when comparing them. For instance, because blue zircon is dense, it's typically heavier than blue topaz. This means that zircon gems will likely be smaller than topaz gems of the same weight. Both gems are susceptible to abrasions and breakage, making careful handling particularly important. Zircon's composition, more brittle in comparison to topaz, limits the shapes cutters are able to make with the gem.
Differing Cuts
Blue zircon comes in many-faceted brilliant-style cuts, step cuts and mixed cuts. A rare, labor-intensive cut with eight extra facets on the lower portion is so distinct that jewelers dub it a “zircon” cut. This gemstone also comes in the polished but unfaceted cabochon cut. In contrast, less brittle blue topaz comes in a wider variety of cuts, most often in elongated, columnar, oval or pear shapes. However, as a widespread, mass-market gem, it may also come in brilliant, rounded, triangle, emerald, marquise and cushion shapes.
Inclusion Issues
Blue zircon is typically clear and doesn't have inclusions -- or foreign particles enclosed in the gem -- though untreated gems may have a slightly cloudy or smoky appearance. Very rarely, you may come across parallel “cat's-eye” inclusions on cabochon-cut stones. Fashioned blue topaz also typically lacks inclusions. Inclusion affects price across the board -- clearer gems fetch more money -- but jewelers typically offer blue topaz at a significantly lower cost than blue zircon. As of 2014 prices, zircon of the same carat as topaz may retail for three times the price or more.