Tanzanita: Guia del Comprador
[Fuente: http://www.diamond-guide.com/Color_Stone_Guide/Tanzanite/tanzanite_color.html & otros]
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Tambien denominado Zoisita azul
Descubierta a principios de 1960 en Tanzania, Africa del Este. Tiffany & Co. denomino a la zoisita azul como "Tanzanita" en honor de su lugar de descubrimiento y comenzo a comercializarlo en 1970.
Well known for their predisposition for virtually flawless clarities, enhancing sparkle, brilliance and ultimately beauty. While it would be incorrect to say tanzanite is a clean gem species, with so many near flawless tanzanites available on the market, obtaining such top quality clarities is within everyone's grasp - something that cannot be said of ruby, sapphire or emerald.
Did you know that tanzanite was originally introduced to market as a sapphire substitute? It's true. Tanzanite wasn't discovered until the 1960's! And what began as a second string replacement has blossomed into one of the greatest success stories in gemstone history.
Even though tanzanite still sells for far less than sapphires and other gemstones, it is quickly becoming respected and prized for its unusual clarity and brilliance.
Unlike diamonds, rubies and emeralds, for which there are mines the world over, tanzanite is found only in Tanzania, Africa.
Tanzanite is actually classified in the gem world as a three-colored gem. So when you see deep blue, flashes of purple and shades of violet in one stone, you are observing qualities that any sapphire would be thrilled to claim, but they are exclusively tanzanite's.
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Now, have fun, and fall in love with this beautiful stone from the heart of Africa.
Tanzanite is classified as a three-colored gemstone. The highly prized deep-dark blue is hard to find in tanzanite under two carats. Tanzanite is the most difficult gemstone to match. Jewelry requiring more than one stone can be a challenge.
When it comes to color, tanzanite is one of the trickiest gemstones to judge. Of course, the color of all gems shifts slightly under varied lighting conditions. But tanzanite not only changes color under different light, but it can also display several shades of color at once. Therefore it is important to examine tanzanite under many light sources so you know what shades to expect from a particular stone. After you determine the many tones, look at the stone again under a neutral-fluorescent light (which best mimics mid-daylight) to make the final judgment of the predominant hue.
So what is the ideal color for tanzanite? And how should you go about examining this chameleon of a gemstone? Here's a few pointers:
Since tanzanite began its career as a substitute for blue sapphire, and because blue is the most popular color for any gemstone, deep-dark blue is considered tanzanite's most desirable hue. Keep your desired color range in mind when evaluating each stone. Some will emit purple and violet tones, others may tend more toward reddish or orange. Think in terms of hue, tone and overall purity when examining any gemstone. Remember that tanzanite is classified as a three-colored gemstone, so determining the hue and purity can be tricky. Examine the stone from the top, sides and bottom under each lighting source. The strongest color under all tests will be the hue of that particular stone, the most consistent secondary colors will determine the tone, and the lack of gray and brown will fix the purity. It is important to note that the most valuable dark-blue color is hard to find in tanzanite under two carats. Also remember that because of tanzanite's intrinsic trichroic (three-colored) nature, it is one of the most difficult gemstones to match. This becomes a bigger factor if you are considering tanzanite for earrings or other jewelry where more than one stone will be used. If you are buying a stone with the intention of reselling at some point, you should try to find the deep-blue of highest quality. However, if you are looking for a tanzanite to match your eyes, wardrobe or skin tone, you can afford a little more freedom in your decision.
Tanzanite is typically the most transparent of all gemstones. Always wipe gemstones with a soft cloth before examination. Look out for cracks that could threaten durability.
Like all gemstones, clarity is the term which describes how free from flaws a given stone is. Flaws are identified in two categories. Internal flaws [called inclusions] and external flaws [or blemishes]. Tanzanite is probably the most transparent or "eye-clean" (free from visible flaws) of all fine gems. Because of this, the tolerance of visible flaws in tanzanite is greatly reduced compared to other gemstones.
There are many types of flaws inherent in tanzanite, most of which are harmless. The only thing you need to look out for are cracks which could greatly weaken the stone, or dark blotches that block light passage, hence clarity.
The same method of investigating tanzanite for color quality can be used to qualify its clarity: examining from multiple light sources and angles. You're looking for inclusions and blemishes which won't be visible from all angles. These flaws can have a detrimental effect on the stone's overall transparency and uniformity of color dispersion. Look from top, bottom and sides under overhead lighting, first with the naked eye, then through a 10X loupe. Next, examine the stone from all angles with light shining through the sides. Here's a couple more handy tips:
Always clean stones with a soft cloth before examination. Oil and dirt can block transparency. Only compare tanzanite with other tanzanite, and only with the same quality, cut and size. It's best to purchase any gemstone loose. Settings can hide flaws and make grading of clarity and transparency very difficult.
Round and trilliant cut tanzanite will cost more than other cuts. Examine the stone from all sides; think symmetry and proportion. Look out for large "windows" on top of the stone and off center "culets" (bottom points.) These are sure signs of low quality.
Tanzanite is available in a wide variety of cuts and styles. From a simple cabochon (dome shaped) cut to elaborate carvings, you pretty much have free reign to choose whatever style suits your fancy.
Although cut and style play a far smaller role in valuing tanzanite than do color, clarity and carat weight, there are a few cutting/style factors that will affect the cost of your stone.
Expect to pay a higher price for trilliant (a "brilliant" 58 faceted triangular cut) or round cut tanzanite than pear shaped or emerald shapes. This is due to the unavoidable loss of rough stone in cutting such refined shapes. Because of naturally high transparency in tanzanite, many top European designers take extra time exploring unique faceting concepts to see just how brilliant their luster can be. These cuts will demand top dollar as well. Keep in mind that lower quality stones will almost always be priced alike, regardless of cut and style.
So, just how do you go about judging the quality of cut in tanzanite? As with any gemstone, the best way to evaluate workmanship is to look at a lot of stones. As you examine the stones, think of these things:
Ask your jeweler to explain the many terms used to define cut and style. Think in terms of proportion and symmetry. Can you read the newspaper through a large "window" when looking directly into the top of the stone? That's not good. Large windows used to be popular and are still found in antique jewelry, but modern styles attempt to de-emphasize such effects. Also when looking through the top, look for dark spots (called extinction.) You will almost see some areas of extinction, but with tanzanite, this should be minimal. Is the culet (bottom point) centered? Very important. Observe the stone from the profile. Think overall depth. You don't want the crown (top) to be too high, or the pavilion (bottom) to be too deep. The best way to envision proper depth, keep the image of diamond profiles you see all the time in mind, like those used for grading hotels, jeweler's advertisements, etc. That's the paradigm of good depth percentage.
Always think in terms of "cost-per-carat" Only compare stones of equal size, shape and overall quality The most desirable color for tanzanite is usually not possible in stones under 2 carats.
Simply put, a carat is a carat is 1/5th of one gram. There is one tanzanite specific issue when it comes to carats. That is that due to their transparency, the smaller stones will tend to be fairly light in color. Since deep-dark-blue is the most valuable color for tanzanite, if you are looking for that color, you may have to limit your search to stones over two carats. The good thing is that tanzanite is relatively inexpensive in gemstone terms, so a top-quality two carat tanzanite would still cost substantially less than a sapphire of the same size. Other than that, the following carat rules apply to all gemstones:
Think in terms of "per-carat cost" rather than total cost. This is because price per carat varies depending on scarcity of stones, quality of a stone, popularity of a stone or cut, etc. When shopping for set stones, beware of "total weight" labels. Always determine the weight of the stone before it was set. Due to the variability of cost per carat factors, always compare stones of the same size, cut, and overall quality. Remember that tanzanite stones under 1/2 carat are generally priced by millimeter size, not by carat weight. Just because a carat is a carat, doesn't mean that one carat tanzanite is the same size as one carat anything else. Different stones have different densities and should only be judged amongst themselves. Even then, cut can have an illusory effect, so compare matching cuts as well.
Tanzanite: Characteristicas - [Fuente: http://www.faceters.com/properties/tanzanite.shtml]
Color: Blue, violet, purple, orange, brown, colorless, pink and also some collector colors Mohs Hardness: 6-6.5 Refractive Index: 1.691-1.70 Critical Angle: 36.28? Specific Gravity: 3.10-3.37 Cleavage: Perfect in 1 direction Fracture: Uneven, brittle Dispersion: Moderately high (.030) Heat Sensitivity: Moderate Pleochroism: Trichroic - strong. Blue to purple to orange or brown Birefringence (double refraction): Weak (.006-.009) Crystal Structure: Orthorhombic.
Precios Orientativos alcanzados en subastas recentes: