Tanzanite

Hailed as the “gemstone of the 20th century”, Tanzanite was discovered less than 50 years ago and has rapidly acquired a worldwide reputation as a rare and precious gemstone. Strong and growing demand, especially for superior quality crystals and those that are fairly large in size, has a direct influence on the price of Tanzanite. The steady price increase is also due to the rarity of the gemstone, as it is only found in one place on earth.

Tanzanite is an extraordinary gemstone, endowed with a marvellous colour: ranging from ultramarine blue to sapphire blue, surrounded by a delicate, purplish halo. Tanzanite can also be recognised by its strong trichroic effect. It diffuses different colours depending on the angle from which one looks at it: blue, violet and burgundy red, adding subtle depths to its colour.

Rarely a pure blue, Tanzanite is distinctive for its harmonious purples and violets. In smaller gemstones, Tanzanite tends towards lighter shades of lavender and periwinkle blue. Large stones tend to shine with more intense colours, fires and brightness.

Rough Tanzanite gemstone should be the least included possible, otherwise there is a risk of fissure. In fact, working with Tanzanite can be a headache for even the most experienced cutter, as the cleavage of this gemstone is quite pronounced in one direction. Tanzanite can be cut into every imaginable shape, from the classic round shape to the most imaginative of cuts. At the moment the city of Jaipur in India has the largest Tanzanite cutting centre in the world and 80% of all gemstones are cut there.

Tanzanite is the birthstone of people born in December.

Discovery of Tanzanite

Tanzanite takes its name from Tanzania, a country in East Africa where the only vein known in the world was discovered in 1967. Millions of years ago metamorphic schists, gneisses and quartzites formed impressive inselbergs with flat summits on the vast plain that lies at the foot of Kilimanjaro. Precious crystals grew in the deposits inside this unusual landscape. For a long, long time, they were hidden from the human eye, until the day when Masai shepherds passing there noticed some crystals shining in the sun, and decided to take them away with them.

The story goes that the effect of heat upon Tanzanite was discovered when a few crystals of brown zoisite that were scattered on the ground in the midst of other stones were caught in a fire caused by lightning that ravaged the green hills of Merelani in north east Arusha. The Masai farmers who brought their herds to the region noticed their beautiful blue colour, gathered the crystals and thus became the first collectors of Tanzanite. 

The gemstone was accepted by the Geological Institute of America (G.I.A.) as a type of zoisite and this recognition was backed up by other influential universities and museums. In reality, the first person who correctly identified this gemstone was a geologist working on behalf of the Tanzanian government. He brought two faceted stones to Henry Platt from Tiffany & Co., who was very impressed by their beauty and dubbed them “Tanzanite” - a name which rapidly caught on in the business.

Today, the foothills of Mount Kilimanjaro remain the only place in the world where Tanzanite can be found. The Tanzanian government has limited the mining area into four blocks – A, B, C and D – over an area measuring roughly 5 km by 2 km. The largest Tanzanite in the world was found in August 2005 in the Block C mine. The crystal weighed 16.389 carats (3.4 kg) and measured 22 x 8 x 7 cm.

Tanzanite Value and Treatment

Like most gemstones, the price of Tanzanite depends largely on its colour, size, clarity and, of course, the number of carats. The most sought-after colours range from sapphire blue to intense blue violet. A paler violet tone is also popular and remains relatively affordable. It goes without saying that the value of Tanzanite, which is a transparent gemstone, changes in relation to its clarity. The fewer impurities it contains, the more precious it is.

The beauty of a Tanzanite depends to a large extent on the quality of the cut. A perfect cut ensures that the facets of the gemstone reflect the light the best way and diffuse the most brilliance. If the cut is made too deeply or not deeply enough, the brilliance of the Tanzanite will divert from the bottom to the sides of the gemstone, adversely affecting its shine.

The weight of a Tanzanite also plays a considerable part in determining its price, but this is often sacrificed in favour of a perfect deep blue. Tanzanites whose colour is more blue than purple tend to be more costly because the angle of refraction of the blue light is diverted to the width of the crystal rather than its length. This means that if a cutter chooses to optimise the purity of the blue colour, the gemstone cut from the rough material will be smaller and will cost more per carat. However, this blue is so handsome that the sacrifice is often worth it. Because of its rarity and the precision required to cut them, the largest Tanzanites by necessity attain higher prices.

Today most of the Tanzanites found on the market are heat treated to enhance their colour. The large majority of rough crystals of Tanzanite have a high proportion of yellow and brownish hues, which disappear when they are heated to approximately 500°C. This heat treatment of Tanzanites is a practice that is quite common and accepted in the trade.