As the name suggests, tanzanite takes its name from the country where it was discovered: Tanzania. This country was populated by a nomadic tribe living in the vast plains that stretch to the foot of the well-known dormant volcano, Mount Kilimanjaro. In the 1960s, severe thunderstorms swept across the merelani hills near Kilimanjaro, starting bushfires and causing the Massaï tribe to flee. Once they returned, they discovered blue pebbles on the ground. Originally grey-brown, they had been transformed by the heat into beautiful blue gems. To the Massaï, this was a divine sign as this colour was considered sacred. Perplexed as to the nature of this particular mineral, they instructed a local explorer to learn about this precious crystal found on their soil. Unable to identify it, he referred them to a gemologist in northern Tanzania, who in turn sent them to his father in New York for its analysis at the Gemological Institute of America (GIA). It was this mineralogy research centre, a world reference in the field, that determined that it was a major discovery: a zoisite group that was until then unknown.
Zoisite is a mineral officially introduced into the mineral classification in 1805 by German gemologist A.G Werner, in homage to the Enlightenment thinker Sigmund Zois (1747–1819). However, it was then known only as a brownish mineral, and it appeared that it was due to their exposure to a temperature of 600 degrees that the Tanzanian mines’ gems had taken on this unique purple-blue colour. It was only a few years later that the owner of the well-known New York jewelry store Tiffany and Co were enamoured with them and named them tanzanite, in tribute to their country of origin.
Its mineralogical definition states that it is a transparent zoisite (scientific formula: Ca2 Al3 – SiO4 – 3 OH), a mineral itself from the silicate family. Its traces of chrome and vanadium naturally give it colours that range from azure to purple. Its characteristic deep blue comes from exposure to high temperatures. As a result of volcanic activity in the Kilimanjaro mountain range, this mineral was formed more than 600 million years ago in shale, gneiss and amphibolite derived from the metamorphism of calcic rocks. The gem’s hardness can vary from 6 to 6.5 on the Mohs scale. Its density is 3.15 to 3.37 and the main refraction indices are 1,685; 1.688; 1.697. The dimensions of tanzanite crystals vary, but the weight of gems rarely exceeds 100 grams.
Displaying no fluorescence, its unique lustre comes from the strength of its pleochroism (the ability to change colour depending on its orientation). As for this mineral, it even displays trichroism, meaning the crystal has three colours: blue, red-purple and yellow-green brown (bronze). The intensity of each of these colours depends on the angle of observation of the crystals. Naturally endowed with these three colours, tanzanite is cut to a particular size to highlight its blue. Indeed, faceting is not done by length but by width to decrease the purple and violet aspects and accentuate the purity of its blue. These varieties are the most sought after. There is a multicoloured variety known as ‘fancy’, the most famous of which is called ‘chameleon’ for its multicoloured reflections. The high degree of transparency and absence of inclusions distinguish tanzanite stone.
A thousand times rarer than diamond, tanzanite is only extracted in a single part of the world. Indeed, if zoisite is found in different countries such as Austria, Switzerland, Italy or the United States, there is only one place of extraction for tanzanite… And it measures just 20 km²! Estimated reserves are only 105 million carats (cts), a total weight of just 21 tonnes. They will deplete in around 20 years according to scientists’ estimates.
Though this natural mineral is not classified as a gemstone (which includes diamond, sapphire, ruby and emerald), its rarity and price, of course, make it highly sought-after by jewellers and jewellery admirers around the world. The most famous gem weighs 242 carats (cts) and is called ‘Queen of Kilimanjaro’. It adorns a beautiful tiara with 803 tsavorites and 913 diamonds created by Tiffany Jewelry. Today, it is part of Apple’s CEO Michael Scott’s private collection.
This precious natural mineral is associated with creativity and imagination, making it the perfect ally for artists. It increases intellectual curiosity, artistic creativity and literary talent as well as humour. It therefore affects the brain and the senses: it is also very beneficial for sight and hearing. Stimulating extrasensory perceptions and intuitive qualities, it promotes spiritual searching and contemplation.
It is associated with the astrological signs Aquarius, Gemini, Aries, and Pisces and above all, Capricorn, as it is the stone of December. It is also the symbol of the 24th wedding anniversary.