In our newsletter this month:Understanding Gem Treatments
Rough Sapphire from Madagascar
If you're new to buying colored gemstones, one of the first things you'll learn is that many gems have been treated or enhanced in some way - heated, fracture-filled, irradiated or dyed, to mention just some of the common treatments. This leads many buyers to wonder, Should I buy a treated stone? Or should I spend more and get a truly natural gem? This month we begin a series of articles on understanding gem treatments.
Here is one response to the question: Gemstones are a wondrous product of nature, and their natural beauty should not be enhanced or improved in any way. Some say that if you don't care about buying a truly natural product, you should buy a synthetic or a treated gemstone. But only nature can produce a true ruby, sapphire or emerald.
Many gemstone buyers would endorse this point of view. But it is actually quite naive. After all, you don't see many people wearing unprocessed minerals on their fingers or around their necks. We expect natural minerals to be improved by skillful cutting and polishing. Gems don't come out of the ground with a facet cut! If you've seen rough, uncut sapphire (see the photo above for an example) you were probably amazed that a brilliant blue sapphire could be produced from that clump of dull aluminum oxide crystals.
As we think about this further, we realize that gemstones are a product of the human crafting of natural materials. The pertinent question is, what kinds of enhancements are acceptable? And how do these enhancements affect the price and value of a gemstone?
One common misconception is that only inexpensive gems are treated. However, many valuable gem varieties are routinely treated. Tanzanite, for example, is an increasingly rare and valuable gem. A great deal of the tanzanite on the market is heat treated, since untreated tanzanite can have brown or yellowish tones. The heat eliminates these undesirable hues and enhances the blue-violet color. The situation with emerald is similar - even very expensive emeralds are oiled to fill fractures that are characteristic of the raw material. Many relatively inexpensive gem varieties, on the other hand, are rarely, if ever, treated. Garnet, amethyst, peridot, fire opal, fluorite, iolite, moonstone, quartz and prehnite are just some of the many gemstones that are almost always untreated.
There are two main reasons why gemstones are treated. In the case of some gems, the treatment is essential to the gemstone's character as we know it. Blue topaz, for example, would not exist in vivid colors without irradiation treatment, since naturally occurring blue topaz is virtually nonexistent and has very subtle colors. Similarly, the characteristic banded patterns of many agates would not be so striking if these gems were not dyed using methods first discovered in ancient Rome.
The other reason why gems are treated is to improve their color and clarity. In the case of a gem like emerald, the raw material tends to be quite included and fractured, and filling the fractures with oil or resin greatly improves the appearance of the gem. Thus fracture-filling has become a standard treatment for nearly all emeralds. In the case of ruby and sapphire, untreated stones of good color and clarity do exist, but they are increasingly rare and expensive. So heat treatment is used to improve the color and clarity of lesser quality material.
The value of a ruby or sapphire enhanced by heating is, not surprisingly, lower than that of an unenhanced specimen with the same color and clarity. Unenhanced gems, of course, are extremely rare. Without the enhancements produced by heating, the supply of eye-clean ruby and sapphire of good color would be so limited that these gems would be available only to a tiny number of wealthy customers. So gem treatments are a way of dealing with market realities - the fact that the supply is scarce and demand is high.
Next month we'll look at heat treatment in more detail; how and why it works, how it can be detected, and how it affects the integrity and stability of a gemstone.New in Gems
Our buyers are always busy searching for the best value gems for our customers. Here are some of the excellent buys we've made in the last few weeks:
Each month our staff select some of their favorite gemstones from our inventory. This month we feature some rare and unusual large pieces from our recent acquisitions. Click on the photos to go to the product pages.
Gemstones Worth Knowing
Each month we focus on one of the lesser known gemstones. This month's featured stone is andalusite.
Andalusite is a strongly pleochroic gem, which means that it displays different colors when viewed from different angles. While it is a strikingly beautiful gem, it is largely unknown by the gem-buying public. With a hardness of 7 to 7.5 on the Mohs scale, it is suitable for all kinds of jewelry.
Its pleochroism means that it shows shades of brown, green and reddish-brown, depending on the viewing angle. This can be enhanced by specific orientation and cut. Cuts with a long axis, such as an oval, marquis or emerald-cut, tend to show one color near the center and a second, usually darker color near the ends of the gem. Square and round cuts usually blend the colors into a mosaic. Most specimens contain some inclusions, the most common being rutile needles. Brazil is the chief producer of andalusite, but Sri Lanka, Russia, Spain and the USA also have deposits.
For more information see our andalusite info page.Customer Questions
Every month we answer questions of general interest from our customers. Please feel free to send your questions to firstname.lastname@example.org, with "newsletter question" in the subject line.
A final note - if you send us email, please be assured that we answer all our email very promptly, 6 days per week. But we sometimes have problems with spam filters on the receiving end, so please adjust the settings on your email account so that you can receive email from email@example.com.
Happy gem hunting!
Your friends at GemSelect
- First Published: September-01-2007
- Last Updated: November-06-2014
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