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Zircon is an important gemstone of many colors, and is an historical gemstone used for thousands of years. It is sometimes looked upon as a cheap Diamond simulant, but in actuality it can be a valuable gem. Its color diversity is caused by traces of certain impurities, some of which are radioactive. Zircon gemstones containing radioactive element traces undergo a process called metamiction, in which their inner crystal structure becomes destroyed. These radioactive forms of Zircon must be heated to stabilize them for use as gems. In fact, many of the gem forms of zircon (even those that are not radioactive) are heat treated to enhance color and increase transparency. The radioactivity in Zircon gemstones is very minimal and is generally believed to be safe, without posing any health hazards. |
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Chemical Formula |
ZrSiO4 |
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Color |
White, Colorless, Blue, Red, Green, Yellow, Orange, Brown, Pink, Purple, Gray |
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Hardness |
7.5 |
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Crystal System |
Tetragonal |
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Refractive Index |
1.930 - 1.987 |
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SG |
4.6 - 4.8 |
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Transparency |
Transparent |
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Double Refraction |
.059 |
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Luster |
Adamantine |
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Cleavage |
3,2 |
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Mineral Class |
Zircon |
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Zircon comes closer to resembling Diamond than any other natural gem. Its strong luster and intense fire gives it a real sparkle that is comparable to Diamond. However, its popularity is somewhat diminished by the fact that it is often perceived as an inexpensive Diamond imitation. Colorless Zircon is easily distinguished from Diamond by its strong double refraction and lower hardness.
The brilliant luster and fire of Zircon, combined with its good hardness and range of colors, make it a most desirable gem. However, it does have some undesirable traits. An interesting and strange habit exhibited in only few Zircons is that their color darkens and their luster dulls upon prolonged exposure to sunlight. This effect can be reversed by giving the stones a second heat treatment. Zircon is also prone to cracking and chipping if banged too hard. For this reason, care must also be taken when faceting Zircon gemstones. Another important factor when faceting Zircon is to minimize the appearance of its strong double refraction by cutting along proper angles. Zircons that are not faceted propely can appear blurry, due to strong double refraction.
Zircon is sometimes confused with Cubic Zirconia. Cubic Zirconia, a synthetic, inexpensive Diamond simulant, resembles colorless Zircon and has a similar sounding name. However, the two are entirely separate substances, and have no connection with each other except for the fact that they both contain the element zirconium in their chemical structure.
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Zircon of all colors are used as gems, but blue, golden-brown, and white are the colors most often used. Blue Zircon, the most popular color, has a lively pastel blue, and occasionally has a very desirable striking bright blue color. Colorless Zircon is usually cut with a brilliant cut to bring out its fire to its fullest capability. It is often used as a cheaper, yet natural alternative to Diamond. The other color forms (yellow, green, pink, and purple) are less often seen in jewelry.
Zircon is the traditional birthstone for December.
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Jacinth
- Yellow, orange, brown, or red variety of Zircon. Also synonymous with Hyacinth. Though the terms Jacinth and Hyacinth are no longer used in the gem trade, they are historically important names going back to biblical times. In ancient times, before there were mineralogical classifications for gemstones, the term Hyacinth may also have referred to an orange or brownish Topaz.
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Jargon
- Colorless, pale gray, or pale yellow variety of Zircon.
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Matura Diamond
- Trade name for colorless Zircon.
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Starlite
- Blue gem variety of Zircon. The color of Starlite is rarely natural, and is almost always heat treated.
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Zircon gemstones are often heat treated to produce good coloring and increase transparency. Heating semi-transparent, grayish-brown or reddish-brown Zircon from
most localities in an oxygen-free environment will give it a blue color.
If these blue stones are then re-heated in air, their color turns
golden-brown. Heat treatment of certain Zircon gemstones also produces
colorless gems. Almost all blue and colorless forms of Zircon are heat treated.
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Zircon sources include Cambodia, Burma (Myanmar), Sri Lanka (Ceylon), Australia, Tanzania, Mozambique, Madagascar, Nigeria, Pakistan, and Afghanistan.
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Because Zircon occurs in so many colors, there are many gemstones that resemble it.
Colorless Zircon resembles Diamond. It also resembles synthetic Diamond simulants such as Cubic Zirconia and Strontium Titanate. It is distinguished from these and other colorless gem forms by its strong double refraction.
Blue Zircon can be similar to Aquamarine, Blue Topaz, Blue Tourmaline, and Blue Spinel; Golden-brown Zircon can be similar to Topaz, Citrine, and Sapphire; Yellow zircon can be similar to Yellow Diamond, Yellow Sapphire, Golden Beryl, Chrysoberyl, and Topaz; and Pink Zircon can be similar to Rose Quartz, Morganite, Kunzite, Spinel, and Pink Topaz.
The luster, fire, and double refraction make Zircon gemstones distinguishable from most others.
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