It is possible to buy Tanzanite in a myriad of different places and mediums in this age of communication. One of the more recent and possibly most risky of places is the internet. It offers up a virtual cacophony of opportunities to purchase this much revered gemstone but no benchmark as to what is a good buy and what is not. This article endeavours to arm the reader with a working knowledge of what they should be looking for when attempting to buy a Tanzanite, either on the internet or in a more traditional setting such as a jewelry store.
When purchasing Tanzanite there are several main factors you need to consider - these are the 4 c's - Color, Clarity, Carat Weight and Cut.
COLOR
Color is the most important of the 4 C's when considering Tanzanite quality. It can also be one of the most confusing aspects as you surf the web as so many different sites use different terms/grading systems and it is difficult to effectively compare one with another.
COLOR GRADING SYSTEM
There is only one universally accepted official grading system for colored gems and that is the GIA system (Gemological Institute of America). However, there are numerous trade based systems as you will see when surfing the web. The majority of these are very subjective and vary widely. One of the terms commonly used (and misused) in the trade is AAA Tanzanite. This is a term used by the miners to denote the very top grade of Tanzanite - the very deeply saturated exceptional stones. Only 1% of all Tanzanite is this grade and this very deep color saturation is very hard to come by.
The GIA grade for these stones is bV 6/5 and vB 6/5. As color is such a visual medium I cannot give an adequate synopsis of the different color grades in this article but there is a very useful resource on the Lapigems Gem Company website by clicking on the various links under the heading "Tanzanite Education" on Lapigems Gemstone Company website. You will be treated to a multimedia presentation using moving pictures which will give you a very good visual exposure to what to look for in terms of color as well as tone and saturation charts illustrating how the GIA system works with color and what to look for in terms of how it applies to Tanzanite.
I will now move on to the second most important consideration - clarity.
CLARITY
Clarity is the second most important of the 4 c's when considering Tanzanite quality. Clarity simply refers to how inclusion-free a gemstone is. Once again, the most universally accepted and most documented system is the GIA system but there are also numerous other trade based systems in use. The basic rule with Tanzanite is that it should be at least eyeclean but preferably loupeclean too. Top stones are loupeclean. Below is a chart showing the GIA clarity grading system.
VVS VS SI1 SI2 I1-3
VVS: This is the top grade in the GIA system. Tanzanite is classed by the GIA as a "Type 1" gem which means it is graded very strictly. Stands for Very very slightly included and whilst most VVS Tanzanites are flawless they can contain minute inclusions which are difficult to see with a loupe (10x magnification) and invisible to the unaided eye. Typical minute inclusions may be very fine needles, tiny hairline feathers, very faint clouds and percussion marks.
VS: This stands for Very Slightly Included and these stones are characterised by minor inclusions which are somewhat easy to see under 10x magnification but usually invisible to the unaided eye. Typical inclusions may be small included crystals, liquid inclusions, fine needles, small feathers
SI1 - SI2: This stands for Slightly Included and these stones are characterised by noticeable inclusions which are apparent under 10x magnification. In SI1 they are usually visible and SI2 quite visible to the unaided eye. Typical inclusions are included crystals, large liquid inclusions, feathers, dense clouds.
I1-I2-I3: The lowest grade. Stands for Imperfect. These stones are characterised by inclusions that have a negative effect on either appearance, durability or both. At I1 there is a moderate effect on either factor, I2 a severe effect on either factor and I3 a severe effect on both factors.
In terms of Tanzanite, a top stone must be VVS. Any lesser clarity grade will affect the value downwards and denotes a lower grade stone.
CARAT WEIGHT
Tanzanites exist even in the 100+ carat range but these are rare. Generally stones are in the below 1 - 10 carat range. Carat weight affects the price generally as weight increases stones in the same quality bracket will cost more per carat.
CUT
Although it has the least impact on value of the 4 C's cut is still important. In the market, tanzanites are found in a variety of shapes and cutting styles. Ovals and cushions are the most common, but rounds are also seen, as are other shapes, including emerald cuts, trillions, etc. Cabochon-cut tanzanites are not often seen. Cuts should be proportional - you don't want to pay for a stone with alot of weight in the pavilion for example when this weight will be invisible in a setting.
OTHER CONSIDERATIONS
FAKES / SYNTHETICS / IMITATIONS : Tanzanite has never been synthesized, but a number of imitations exist. The most common is blue-violet glass. A synthetic fosterite has also been used as an imitation and is known as Tanzanique in the trade. It has a lower RI than Tanzanite and does not have the same pleochroism so is easily distinguished from the real thing. However, laymen can easily be fooled so always buy from a reputable dealer, preferably a member of the ICA (International Colored Gemstone Association) which has a strict code of ethics.
ENHANCEMENTS: Virtually all gem tanzanite of a blue violet color has been heat-treated to enhance the color. In the rough state most Tanzanite is predominantly brown. Heating at 500 to 600 degrees centigrade causes this colour to change to blue. This is a permanent and stable change.
LIGHTING: A great deal of Tanzanite marketing makes a big deal of the "red flash" phenomenon of Tanzanite. This is one of the features of the stone and is due to Tanzanite's trichroism. Tanzanite is extremely light sensitive, with incandescent lighting (yellow lighting found in common light bulbs) tending to shift its color to the violet side causing the red and pink flashes to appear within the stone.
WHAT IS BLOCK D TANZANITE?: Block D Tanzanite is a term commonly used in marketing Tanzanite. Block D simply refers to the area from which material is mined. The Tanzanite mining area has been divided into 4 blocks by the Tanzanian government - Blocks A to D. Traditionally, larger quantities of the best material was found in block D so the term became synonymous with the top grade. However, it has become a bit of a marketing ploy recently and is a term misused as it implies that only block D produces the AAA grade. This is not the case - AAA comes from all blocks, block D has traditionally just produced more of it than the others. It is best to ignore the term as it is simply a marketing ploy and it is largely misused. It is better to use more scientific and official grades like the GIA system than to rely on subjective trade terms.
This article has tried to cover all the main points that should be taken into account when buying Tanzanite. Undoubtedly there will be others I have missed but if these basic tenets are adhered to and understood, the minefield of Tanzanite purchase should be a safer place.
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