December is another lucky month with two birthstones: Turquoise and Zircon. This newsletter discusses zircon as the lesser-known stone.
In today's marketplace, Zircon comes in many colors, including green, yellow, orange, red, brown, purple, and blue. The wide and varied palette of hues make zircon a favorite amongst collectors and informed consumers.
Colorless zircon was once a common diamond simulant in the 19th century because it has brilliance and flashes of multicolored light called "fire." These two optical properties of zircon were close enough to diamond's optical properties to account for centuries of confusion between the two gems.
The zircon color most associated with the month of December is blue. Blue is the most common color of zircon, more specifically, a lovely greenish-blue referred to in the trade as "zircon blue" (shown in above image and image immediately below). Due to their greater demand, blue zircons usually command higher prices than any of the other color zircon varieties in the marketplace. Because of blue zircon's higher price point, the much more affordable and available blue topaz is often used as a substitute for blue zircon.
In the Middle Ages, zircon was thought to induce sound sleep and keep away evil spirits. It also was a celebrated stone capable of promoting riches, honor and wisdom.
Scholars debate the source of the word "zircon," possibly due to the gem's breadth of natural colors. Some think the word is derived from the Arabic word "zarkun," meaning "cinnabar" or "vermilion," while others think it comes from the Persian word "zargun" or "gold colored."
Gorgeous Color, High Clarity, Typically Heat Treated
The supply of fine zircon is limited. Zircon crystals grow in many different types of rock and possess a range of optical and physical porperties, with some zircon almost completely broken down by radioactive elements present in zircon as impurities. High or normal crystal structure zircons are used as fashioned gems in jewelry.
Zircon is mined in Australia, Cambodia, China, Myanmar (Burma), Sri Lanka, Thailand, and Vietnam. The available sizes of fashioned stones typically depend on color. Blue or green zircon normally ranges from 1-10 carats, yellow or orange up to 5 carats, and red or purple in smaller carat weights.
It is a challenge to cut zircon because the gem is brittle, a property magnified by heat treatment (discussed below). Most zircon colors are available in fancy shapes, such as hearts, ovals, marquises and pears. Colorless and blue zircons are sometimes fashioned in a style known as the "zircon cut," a round brilliant with 8 extra facets at the base of the stone to take advantage of zircon's luster and fire. However, this cut is not done very often because of the extra labor costs involved. Though rare, zircon can exhibit the cat's eye phenomenon when cut as a cabochon.
Zircons are relatively free of inclusions, but many untreated zircons have a cloudy or smoky appearance. In Victorian times, this smokiness made zircon a popular gem for mourning jewelry.
Today, most zircon that is faceted for jewelry is free from eye-visible inclusions. Unclean stones cause a drop in zircon value.
Since fine gem-grade zircon exhibits high clarity, it can be fashioned into cuts with large tables that show off color and clarity, such as the emerald cut (shown in above image).
Blue zircon was a particular favorite in Victorian times and often used in very fine gem jewelry from England. Gemologist George Kunz (Tiffany's famed gem buyer) was a notable zircon advocate - he once proposed the name "starlite" to promote the gem's fiery nature, but the name did not become popular.
Colors Produced by Heat Treatment of Zircon
Although typical zircon colors are light and muted, the finest stones have strong, rich colors. The heat treatment of zircon is routine in the industry. Almost all blue and colorless zircons are heat treated. As a result, zircon's blue is almost always the result of heat treatment and it comes in a range that spans from intense deep blue (shown in above image) to differing strengths of greenish blues, from slightly greenish blue to vivid greenish blue. In addition, heat treatment of zircon also can produce yellow, orange, red and brown.
Care and Cleaning of Zircon Gemstone Jewelry
The heat treatment of zircon is generally stable, although some stones revert to their original natural color when exposed to light. As a result, it is best to keep zircon jewelry away from strong light sources for any period of time. Also, heat can alter the color of zircon and so care must be employed when fabricating, cleaning, and repairing zircon jewelry. Heat treatment of zircon presently is not detectable even by a gem lab, but all zircon is assumed to be heat treated because of its prevalence.
Zircon has medium hardness (6-7.5 on the Moh's scale), and it has fair to good toughness. Heat treatment can make zircon brittle and more vulnerable to easier abrasion and even fracturing. As a result, zircon is best suited for earrings, brooches and pendants. When zircon is used in rings and bracelets, it is best housed in protective settings to keep the stones from becoming scratched and abraded.
Although zircon is not susceptible to chemicals, its color can be dramatically altered by heat, and therefore, it is very risky to clean zircon jewelry by ultrasonic or steam cleaning. As is always the case with fine gems, the safest method for cleaning zircon jewelry is with warm, soapy water and a soft cloth. Also, because zircon can be easily abraded, it is not safe to use any abrasives or brushes to clean zircon jewelry.
Blue Zircon & 14kt White Gold Necklace by Robert Lang
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