Zircon Buying Guide
Long valued for its brilliance, zircon is a natural and affordable beauty. Often confused with cubic zirconia, a synthetic diamond substitute, zircon remains unfamiliar to many buyers. However, with colors spanning the rainbow and colorless stones that outshine even mid-grade diamonds, this December birthstone makes an excellent addition to any jewelry collection.
Zircon Buying and the Four Cs
Since zircons come in all colors of the rainbow, jewelry buyers and gem collectors have many options.
Blue zircons are the most popular, and their prices reflect this trend. Occasionally called starlite or stremlite, blue hues are almost always the result of heat treatment, which creates a stable color. Blue zircons often have strong green components that give the stone a unique hue. Fine blue zircons exhibit strong green hues and medium tones.
Extremely rare green zircons are a collector’s item. Most green zircons have brownish hues and may have a khaki color. Bright green gems are extremely rare and are the top color for green zircons. Heat treatment of these gems can lighten the hue and restore clarity to the crystal. Zircons with green hues are sometimes called “beccarite.”
Yellow, orange, and red hues are less popular than blue. Thus, they have lower prices. Trade names for yellow zircon include “melichrysos” and, for pale yellows, “jargoon” or “jargon.” The popular “golden” and “honey” hues are often the result of heat treatment. “Hyacinth” or “jacinth” often refers to a transparent reddish-brown zircon. However, this term may also refer to hessonite, a variety of garnet.
Other colors in the red range include rose, champagne, and cognac. These often display slight to significant brown hues. These autumnal colors are perfect for fall fashion trends and can be completely natural. However, much of the material on the market is heat treated from a reddish-brown color.
Purple zircons obtain their color through radioactivity over long periods of time. Exposure to heat and sunlight bleaches these stones. As a result, they aren’t commonly used in jewelry. Buyer beware: much of the material sold as “natural purple zircon” is, in fact, cubic zirconia. Be especially wary of eye-clean gems, as purple zircons are generally heavily included.
Colorless zircons were once the first choice for diamond substitutes. Here, the confusion with synthetic cubic zirconia arises. While more expensive than cubic zirconia, zircon’s brilliance lends itself to simulating diamond at a fraction of the price. In fact, a high-quality zircon may look better than a low-grade or mid-grade diamond, with far less impact on your wallet. Almost all colorless zircons have undergone heat treatment.
Metamictization: Low, Medium, and High Zircon
Untreated specimens may have a hazy or smoky appearance. In general, this is only acceptable in green zircons. Other colors with smoky characteristics won’t hold high value. This smokiness arises from metamictization. This means that, over geologic timescales, trace amounts of radioactive elements in zircon have deteriorated its crystal structure. This radioactivity, while not strong enough to cause health concerns, makes the once-crystalline zircon amorphous. Oddly, this doesn’t affect the gem’s dispersion. Proper heat treatment allows the zircon to recrystallize, improving clarity.
The terms “low,”“medium,” and “high” refer to the extent of crystallization in the gem, with low zircon more metamict and high zircon largely crystalline. In general, low zircon is green, brown, or orange in hue, while colorless, blue, and brownish orange are common colors for high zircon. Medium zircons can be brownish green or dark red.
High zircon frequently appears in jewelry, since it possesses greater hardness than metamict material and doesn’t appear smoky.
You can find zircon in almost any cut. However, brilliant cuts are commonly used to showcase this gem’s brilliance. In fact, the “zircon cut,” a modification of the brilliant cut, uses eight extra facets to flaunt zircon’s high dispersion. Although this cut no longer finds widespread use due to the greater labor required, you will often see it in antique jewelry.
When faceting rough, lapidaries should account for this gem’s birefringence and pleochroism. Facets will appear doubled or fuzzy when viewed through the table. Additionally, zircon rough is often twinned, further complicating gemstone cutting.
Size depends somewhat on color. Red and purple stones tend to be small, while yellow and orange gems are common up to five carats. Blue or green zircons are typically one to ten carats. Price per carat doesn’t rise dramatically for this gem. Very large sizes can be found.
Due to brittleness, older zircon specimens will often show chips along facet edges. Zircon also ranges in hardness from 6.5-7.5, largely due to metamictization. High zircon, such as colorless and blue varieties, has greater resistance to scratching. On the other hand, low zircon, including most green zircon, can scratch more easily. Protective settings and occasional wear will limit damage to the stone.
Almost all zircons receive heat treatments. Fortunately, this treatment is stable and doesn’t require further care for the gem. Very few “high” zircons are found in nature. Heat treatment allows metamict gems to re-crystallize, which improves clarity. Heat treatment can also alter color. For the most popular blue and colorless zircons, heat treatment is applied to brown or reddish-brown rough.
At somewhat lower temperatures, heating produces red and golden colors. Green zircon is commonly “low,” or metamict, and can be heated in order to lighten the color and remove smokiness.
51.87-ct Tanzanian zircon, before and after low-temperature heat treatment. © JL White Fine Gemstones. Used with permission.