When purchasing Tanzanite there are several main factors you need to think - these are the 4 c's - Color, Clarity, Carat Weight and Cut.
Tanzanite Purchasing Tips
Color is the most leading of the 4 C's when inspecting Tanzanite quality. It can also be one of the most confusing aspects as you surf the web as so many distinct sites use distinct terms/grading systems and it is difficult to effectively assess one with another.
Color Grading System
There is only one universally acceptable official grading ideas for colored gems and that is the Gia ideas (Gemological form 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 generally 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 optical medium I cannot give an enough synopsis of the distinct color grades in this report but there is a very useful reserved supply on the Lapigems Gem business website by clicking on the varied links under the heading "Tanzanite Education" on Lapigems Gemstone business website. You will be treated to a multimedia presentation using moving pictures which will give you a very good optical exposure to what to look for in terms of color as well as tone and saturation charts illustrating how the Gia ideas 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 leading notice - clarity.
Clarity
Clarity is the second most leading of the 4 c's when inspecting Tanzanite quality. Clarity plainly refers to how inclusion-free a gemstone is. Once again, the most universally acceptable and most documented ideas is the Gia ideas 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 little inclusions which are difficult to see with a loupe (10x magnification) and imperceptible to the unaided eye. Typical little 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 normally imperceptible 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 normally illustrated and Si2 quite illustrated 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 follow on either appearance, durability or both. At I1 there is a moderate follow on either factor, I2 a severe follow on either factor and I3 a severe follow on both factors.
In terms of Tanzanite, a top stone must be Vvs. Any lesser clarity grade will work on 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 potential 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 range 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 imperceptible in a setting.
Other Considerations
Fakes / Synthetics / Imitations : Tanzanite has never been synthesized, but a estimate of imitations exist. The most tasteless is blue-violet glass. A artificial 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 grand from the real thing. However, laymen can easily be fooled so all the time buy from a reputable dealer, preferably a member of the Ica (International Colored Gemstone Association) which has a precise 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 convert to blue. This is a permanent and garage 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 tasteless 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 generally used in marketing Tanzanite. Block D plainly 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 plainly a marketing ploy and it is largely misused. It is good to use more scientific and official grades like the Gia ideas than to rely on subjective trade terms.
This report has tried to cover all the main points that should be taken into list when buying Tanzanite. easily there will be others I have missed but if these basic tenets are adhered to and understood, the minefield of Tanzanite buy should be a safer place.
Tanzanite Purchasing Tips
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