Brought to popularity by Tiffany and Co in the early 1960’s, tanzanite is a beautiful blue and purple colored zoisite mineral. This trichroic gemstone is composed of the colors blue and purple that can be seen with the naked eye, and a brownish gold color that can only be observed with a device called a Chelsea filter. When tanzanite is mined from the ground, it is a dark brown color and it is not until after the rough stone is subjected to heat that one will see the beautiful colors that tanzanite is famous for.
With so much tanzanite being sold in the Caribbean, many would be under the impression that tanzanite is native to this area. This is a false impression; the only commercial viable source where it is found is in the same place that tanzanite receives its name from, Tanzania, Africa. Tanzanite is a very rare gemstone since it is found in one location and the mines that are producing gem quality stones are producing fewer and fewer each year.
When purchasing tanzanite or any gemstone, the most important quality to look for is color followed by cut and clarity. When judging a stone for color, one would want to make sure that it has the darkest color possible. To get an accurate reading on the color, one should always look at the color along the edge of the stone and not straight down the middle. Other color concepts to be aware of when buying tanzanite or any gemstones are color zones and color bands. Color zones are areas of the gemstone that have a lighter or darker color then the general color of the stone. Color bands are streaks of dark or light colors that run through the gemstone.
The next important concept when buying a good quality tanzanite is the cut of the stone. Cut is important because it brings out the color of a tanzanite and the more color that it displays, the more beauty and value the tanzanite will have. There are three important factors when it comes to cut: symmetry, polish, and windowing. Symmetry is the easiest when determining the quality of tanzanite because one should observe along the outline of the gemstone to see if it is of symmetrical shape. One should also study the tanzanite while rotating it three hundred and sixty degrees to see if the facet junctions are lined up. Next, under an overhead light, one should look at the surface of the tanzanite. The presence of little lines appearing like scuff marks signifies wheel marks from the polishing phase. The presence of these marks takes away from the beauty and value of the stone. The last is windowing of the gemstone. Windowing simply means that one can look through the top of a gemstone and see right through to the bottom.
The final factor when buying a tanzanite is clarity. Clarity is always the last thing to look at when evaluating whether a gemstone is worth buying. Impurities in gemstones cause color and usually with impurities you will have inclusions or flaws within the stone. When dealing with tanzanite, there should be no inclusions because it is a category 1 gemstone. If any inclusions are present, it will have a negative impact on the value of the stone. When observing the clarity inside a tanzanite, one should use a 10x loupe and a flashlight for dark field illumination which is transmitted light from either the side or behind the gemstone. When observing the surface of a tanzanite for any imperfections, one should use a 10x loupe and an overhead light.
Due to tanzanite’s complex chemical structure, the market has not encountered any synthetic tanzanite yet. This does not mean that there are not any imitations or other synthetic stones that are being masked as natural tanzanite. When buying tanzanite in the Caribbean or anywhere else in the world, one should be aware of synthetic forsteritem, polysilicate, and YAG or yttrium aluminum garnet. These three knock-offs may look like natural tanzanite, but can easily be separated with a simple device known as a Chelsea filter. Under a Chelsea filter the synthetic forsteritem has no reaction, polysilicate and YAG have a bright red reaction, and natural tanzanite has a golden brown reaction.
Tanzanite is a very rare an aesthetically pleasing gemstone that will become less available in the future. If one has the opportunity to purchase gem quality tanzanite from the Caribbean at a price much lower than any other location, one should not let that opportunity pass.