Tanzanite is available throughout the globe, and along with prices the grading of stones varies from supplier to supplier. Some use clever marketing ploys in an attempt to entice uneducated buyers to purchase stones from them by using terminology such as ‘D'Block Tanzanite', whilst others use questionable grading systems which present parameters that really do not make much sense, other than to glorify the stone to an absurd degree of high quality. This article will thus attempt to offer you an unbiased guide in the hope that it can help you in your future purchases of Tanzanite.

When purchasing Tanzanite there are several primary factors that you will need to consider. These relating to Colour, Clarity, Carat Weight, Cut (The 4 C's) and certification.

COLOUR & GRADING SYSTEMS:

Colour is of course the most important of the 4 C's when determining the quality of a Tanzanite stone. However, it can also prove very confusing when comparing the stones of one Tanzanite dealer compared to the next, especially if you are looking on the internet, since the differing terminology coupled with often confusing grading systems makes comparison virtually impossible.

As we have already seen there are a multitude of Tanzanite grading systems in use but it should be noted that as yet there is no universally accepted method of grading the stone. Even the world's most recognised laboratories have yet to reach consensus on terms used for grading Tanzanite although the top grading on most systems tend to be similar.The grading system recommended by the Tanzanite Authority and Tanzanite Gemstone is that of HKD Diamond Laboratories in Canada, a progressively thinking laboratory with offices in Canada, Thailand and India (all of which are trained by the GIA).

Grading of Tanzanite is based upon three main criteria; Hue, Tone, and Saturation. Hue refers to the face up colour of the stone when seen at first glance. Tone: refers to how light or dark the colour of the stone appears at first glance and Saturation: refers to the strength or intensity the colour appears.

Simply put, when we talk about the colour of Tanzanite, the best stones which represent only 1% of all output will be Intense in colour (commonly referred to as AAA Grade). The stones will be deeply saturated, with a very deep colour. This is the most desirable colour for Investment Grade Tanzanite; however, some people do prefer slightly paler stones, although this plays a crucial role in determining the stones value.

CLARITY:

After the colour of a stone, comes its clarity: which is the second most important of the 4 C's. Clarity simply refers to how inclusion free a stone is. The top grade stones as a rule should be at worst eye clean, but preferably loupe clean (how a stone looks under a microscope). HKD grade the clarity of Tanzanite and other gemstones in two stages:

Firstly, Tanzanite is assigned a clarity type (I, II, III) and then a clarity grade of either IF, VVS, VS, SI, I. The following will provide you with a breakdown of what these terms mean:

VS: This stands for Very Slightly Included and these stones can be determined as having minor inclusions which are slightly easier to see under 10x magnification but of which are usually invisible to the eye.

SI1 - SI2: This grade stands for Slightly Included and is characterised by noticeable inclusions which are apparent under 10x magnification. In SI1 they are generally visible to the naked eye and in SI2 would be quite visible to the eye.

I1-I2-I3: These are the lowest grades of stones and are Imperfect. These stones are characterised by inclusions that have a serious effect on either the stones appearance, durability or indeed both.

CARAT WEIGHT:

Whilst Tanzanite does exist in excess of 100 carats, generally speaking stones range from under a carat to 20 carats or more with AAA Grade stones over 10 cts being viewed as rare. Bear in mind however that the carat weight will also affect the price of a stone with heavier stones fetching a premium.

CUT:

Finally when we determine the value of a stone, we must also look to its cut. The most commonly available Tanzanite's on the market today are Oval, Cushion (although they are becoming increasingly harder to obtain), Trilliant and Pear Shaped stones, with other cuts such as round, emerald, princess and heart shaped stones being exceedingly desirable and rare.

All of the factors above are summarised in how a stone is certified. Indeed, it is never advisable to purchase a stone that is not Independently Certified by a recognisable laboratory such as HKD, as this will effect whether you really have got what you paid for. In house certificates are also not recommended as these are often biased in their findings, and do little more than glorify the stone.

ENHANCEMENTS:

It should also be noted that all Gem Grade Tanzanite is heat treated. This is a permanent treatment, and turns the stone from its original brownish colour to the Violetish Blue that we all adore. This is common practice, and is no cause for concern.

This article was written by Josh Robbins from tanzanite-gemstone.com and by the Tanzanite Authority's Gemmologist Scott Hemming. If you have any questions regarding Tanzanite please feel free to visit our website and we will be happy to help you.