Tanzanite owes much of its beauty to an unusual gemmological property called pleochroism, the ability to exhibit more that one colour. When viewed from different directions, tanzanite can look blue, violet, purple, bronze or even gray. This is because Tanzanite is a trichomic gem. Very few stones are trichomic and this is what makes tanzanite’s very easy to identify. Trichomic refers to three layers of colour. The more common layers are blues and purples but you may also see flashes of red, green, yellow, or even orange. The colour that gemmologists primarily speak of is the deep royal blue. Before a tanzanite is faceted, the gemstone cutter studies the crystal and decides which directional orientation will show the best colour. And typically, most cutters will try to produce a pure blue tanzanite. Unfortunately, cutting to achieve a blue colour sacrifices a lot of weight and results in a smaller and more costly gem. Yet the blue of the well cut tanzanite is so breathtaking that most agree the sacrifice is well worth it. Stones ranging over 4 carats and larger have been known to show the strongest blue colour. Smaller tanzanite’s are usually soft blue, light violet or lilac purple.Tanzanite Facts
Tanzanite is a relative debutante to the world of gemstones with its discovery in the East African country of Tanzania in 1967, and has been heralded by many as the Stone of the 20th Century. Certainly its impact is undeniable, and in 2002 with its elevation to Birthstone for December in many ways crystallised this feeling into a reality. The legendary New York jewelers Tiffany & Co were the first to market the stone as a fine gemstone, in the rarefied echelons of Diamond, Emerald, Ruby and Sapphire, and gave the stone is name.
While Tanzanite is a relatively recent discovery, the gem is the cobalt ultramarine to sapphire blue example of a minerals that was discovered almost two hundred years ago, in the Austrian Alps.
Nearly all tanzanite has been heat treated to produce the striking violet-blue colour, with the natural colour being a rather dull and uninteresting yellow-brown.
With only one economic deposit currently in production Tanzanite is a member of the gemstone endangered species list. Estimates vary, but in all likelihood with consumption continuing at it current levels, the Merelani Hills deposits of Tanzania will be completely depleted within 20 year
Tanzanite while a beautiful stone has a low hardness compared to other gemstones, and should be worn with care in all but designs that prevent the gem from being knocked or scratchedTanzanite – What Causes The Colour
The causal agent in the formation of Tanzanite’s colour is heating. When heated to 400-500 degrees C, the natural yellow and brown tints of the rough vanish and an amazing blue develops. The colour of the highest quality Tanzanite is described at Cobalt Ultramarine. Although a range of colours from ultramarine to a rich Sapphire blue are commonly seen. The most popular colour, and here availability seems to be the determining factor, is a strongly saturated blue, which shows a purplish almost Amethyst subordinate hue
The decision to purchase a Tanzanite is made for many reasons. Uppermost should be what will the resultant pierce of jewellery be. As has been mentioned Tanzanite exhibits a relatively low hardness (6.5-7 on Mohs scale) and having a perfect cleavage is not very resistant to knocks or scratching. Therefore it should be worn with care at all time and preferable in pierces such as earring, and pendant before the choice of an everyday ring is reached. With care a master craftsman can create a ring for daily wear that does justice to the gem and protects is within certain limitations of design.Colour
The most popular colour is a saturated blue with a purple (violet) subordinate hue, often termed in the trade as “Blue Violet”, less desirable are stones with more purple (violet), which can reach a level where the stones are best described as “Violet Blue”. However that said beauty is in the eye of the beholder, and the final choice remands an intensely personal one.Lighting
Tanzanite is trichroic stone, that is to say it exhibits three different colours when viewed along each of the three major axis (x, y & z). This pleochroism from very strong violet blue to brown, means the stone appears different colours, when viewed from different angles. In daylight the appearance of the stone is more blue, while under artificial light a more Amethyst violet colour is seen in the same stone.Clarity
Tanzanite is a transparent Type 1 gemstones as classified by the GIA (Gemological Institute of America), occurring most commonly as eye clean pieces. As such there is no reason to purchase an included piece unless a very large stone is required, than may exhibit minor inclusions.Cut
The stone is cut in all imaginable shapes from classical to modern. The brilliance of the stone can however be enhances with the addition of extra facets on the pavilions of the chosen cut