In our newsletter this month:

   Understanding Heat Treatment
   New in Gems
   Staff Selections
   Gemstones Worth Knowing
   Customer Questions

As part of our continuing series of articles on understanding gem treatments, this month we look at heat treatment.

The heating of gemstones to enhance their color and clarity goes back centuries, probably beginning with the lucky fellow who accidentally dropped his valuable gem in the fire, only to discover the next day that the color had improved. It must have seemed like a kind of alchemy. Even today heat treatment of gemstones is a secret art that is known to very few.

Depending on the type of gem and the heating conditions, heat treatment can lighten or darken the color of a gem, remove certain color tones or improve clarity. Heat treatment is most commonly used with sapphire and ruby, but there are a number of other gem varieties which are enhanced with heat. These include zircon (blue and yellow), apatite, morganite, tanzanite, and blue topaz (in combination with irradiation).

Heat treatment works by changing the nature of impurities in the gem material. These impurities are usually responsible for the color we associate with the gem. For example, a ruby containing a mere 1% or less of chromium will appear pink or red, but in the absence of chromium the pure corundum will be completely colorless.

Since the impurities in the stone typically react to heat at a lower temperature than the gem material, heat can be used to change the chemical state of the impurity without affecting the base gem material.

In some cases, heat treatment will improve the depth of color because heat causes dissolution of inclusions and diffusion of impurities (especially titanium from rutile inclusions) into the surrounding corundum. Because fine inclusions cause some stones to look cloudy, heat treatment that dissolves the inclusions may also improve the clarity of the stone.

The recipes for 'cooking' gems are carefully guarded and there are many variables involved. Temperature is only one variable. Gems may be heated at temperatures as low as 100 degrees centigrade and as high as 2000 degrees (approaching the melting point of corundum). The amount of oxygen in the heating environment is also key: some gems are heated in a reducing (oxygen-free) environment, others in an oxidizing environment.

Heat treatment can generally detected only by trained gemologists who look for changes in characteristic inclusions in gem material like corundum. On the basis of these observations, gemological labs will issue identification certificates that state "evidence of heat treatment is present" or words to that effect.

It is generally agreed that simple heat treatment of gemstones is stable and permanent. This is not surprising since the heat treatment mimics natural processes involved in the formation of gemstones in the earth. Since the success of heat treatment depends on the different melting points of impurities and the base gem material, heat treatment should not affect the the gemstone material itself.

Our buyers are in the market every day finding the best values for our customers. Here are some of the excellent buys we've made in the last few weeks:

• Tanzanite from Tanzania: Tanzanite is increasingly rare and expensive as supplies dwindle and demand continues to be very strong. So we rarely find good deals. But we've just acquired several dozen high quality pieces that we believe are excellent value at the price. These are mainly between 1 and 2 carats in a variety of shapes, with that medium to deep violet blue that is characteristic of fine tanzanite.
  
  
• Opal from Australia: Last week we bought some very nice opals from Australia, including some solid opals in smaller sizes, and some opal doublets in larger sizes.
  
  
• Citrine from Madagascar and Brazil : We always keep a good stock of citrine, but we recently bought some larger pieces (up to 30 carats) that make wonderful pendants. You'll also find some attractive matched pairs and some new lots of smaller pieces.
  
  
• Andesine from The Congo: We've just acquired some high quality red andesine from Africa. Supplies of andesine from the Congo are quite recent, with the mineral found in a range of colors, including red, yellow, champagne and green. We've bought some lovely pieces in orange and red, with excellent luster.
  
  
• Rutile Quartz from Brazil: Rutile (or Rutilated) Quartz is clear or smoky quartz with inclusions of rutile crystals. While most varieties of transparent quartz are valued most when they show no inclusions, rutilated quartz is valued specifically for the lovely patterns formed by the delicate golden needles of rutile inside it. We have just purchased a new stock of this fascinating gem and every piece is quite unique.
  
  
• Blue Zircon from Cambodia: We have just bought some of the finest pieces of Cambodian blue zircon that we've found in a long time, and we live very close to the Cambodian border! We have round pieces and emerald cuts in sizes up to 5 carats, as well as some lots of smaller pieces.
  
  
• Kunzite from Afghanistan: We had sold out our previous stock of kunzite, but have found a new source. We've just bought some first-rate pieces with excellent color saturation, in sizes up to 50 carats, in a variety of shapes. We now have over 80 pieces of kunzite, probably one of the best selections you'll find anywhere.
  
  
• Tourmaline from Mozambique and Nigeria: We are very active buyers of tourmaline and we add new pieces to our collection every week. We now have nearly 400 pieces of tourmaline in stock, in a huge variety of colors, shapes and sizes. We've recently added some stunning pieces in pink, orange and rose tones, with some pieces as large as 10 carats.
  
  
• Fluorite from Namibia: Many new additions to our stock of this colorful mineral, including a number of interesting multicolor pieces and some lovely matching pairs.
  
  
• Peridot from Burma and China: We've expanded our excellent selection of peridot with some excellent new pieces. Our new acquisitions include some interesting pairs and lots in addition to our many larger single pieces.
  
  
• Ametrine from Bolivia: We've added many new pieces to our growing collection of this popular violet golden gem. Our latest additions are mainly in the 2 to 6 carat range, in a nice selection of shapes. These are lovely pieces at a very affordable price.
  
  
• Tsavorite Garnet from Tanzania: Some excellent tsavorite from Tanzania has come on the market recently, with top color and clarity. One of our best buys were some wonderful matched pairs in cushion cut. If you've always wanted tsavorite earrings, here is your chance to create a really stunning pair.
  
  
• Spinel from Burma and Tanzania: We've recently found some of the finest spinel we have ever offered at GemSelect. We've bought a wonderful range of really outstanding colors, especially red, violet, blue and pink. There are some very well cut pieces in larger sizes (2-4 carats), as well as some first rate matched pairs.
  
  
• Apatite from Madagascar: We've just bought some new stock in this hard-to-find gem, including some lovely light green to forest green pieces that we haven't stocked before. A variety of shapes are available, in weights up to about 3.5 carats, including some matched pairs and lots.
  
  
• Sphene from Sri Lanka: We have added some new pieces to our stock of this rare gemstone famous for its remarkable dispersion or fire. These are bright multicolor pieces in interesting shapes and cuts, up to 4.5 carats.
  
  
• Amethyst from Brazil: We've been finding some very good buys in Brazilian amethyst recently, including some excellent matching pairs in larger sizes (up to 9 carats per pair). We also have a nice selection of cabochons in addition to our many faceted pieces.
  
  

Each month our staff selects some of their favorite gemstones from our inventory. This month we feature some of the finest of our recent acquisitions. Click on the photos to go to the detail pages.

Each month we focus on one of the lesser known gemstones. This month's featured stone is Andesine.

There are fashions and trends in the gemstone world, and andesine is an unusual gem that has drawn tremendous interest in the past year. Gemologists have been particularly intrigued because red feldspar is extremely rare, and different stories have been told about the origin of this material. The original material in the market was identified as coming from the Congo, but recently similar feldspar said to be from Tibet has come on the market.

Adding to the slightly mysterious nature of this gem, it is variously known as andesine and labradorite, or as many people now call it, andesine labradorite. It is found in a range of colors, including red, yellow, champagne and green, but the red is the most valuable.

To see all our stock in this intriguing gemstone click here.

Every month we answer questions of general interest from our customers. Please feel free to send your questions to help@gemselect.com, 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 a week. But we sometimes have problems with spam filters on the receiving end, so please adjust the settings on your mail client so you can receive mail from help@gemselect.com.

Happy gem hunting!

Your friends at GemSelect