Tanzanite: A rare December Gem

50 years young

Tanzanite caused a ripple in the gemstone world when it was discovered in 1967, filling a gap in the colour spectrum not previously covered by any other gemstone: violet. Even more remarkably, it was transparent, enabling the faceting of flawless gemstones suitable for fine jewellery. This indigo-violet-blue gemstone was an accidental discovery and, with a little luck and a great deal of marketing, has become one of the most popular blue gemstones in just half a century.  

Pictured is Kat Florence's 423ct Namunyuk tanzanite and diamond necklace, since auctioned to build a school in Nepal. 

Mined in a single location

The most commonly told story of Tanzanite’s discovery speaks of Maasai herders who found blue crystals in the Merelani Hills near Arusha, Tanzania, while tending livestock in the 1960s. They notified a prospector, Manuel d’Souza, who promptly registered mining claims with the government. Initially, d’Souza believed he had discovered sapphire, but the crystals were soon identified as a vivid blue variety of zoisite — a mineral known since the early 1800s, but never before seen in this colour.

Another legend claims that Maasai warriors found the stones after a large bushfire swept through the area. The fire burned away foliage, revealing gemstones on the surface. The intense heat transformed them into an eye-catching sparkling blue. Without the fire, Tanzanite may never have been noticed, as the stones appear brownish in their natural state against the earth.

It has never been found anywhere else in the world.

In the 1970's it was found in two places: Tanzania & Tiffanys

Shortly after its discovery, Tanzanite was brought into the international spotlight by Tiffany & Co., a house known for its early investment in unusual and colourful gemstones. They renamed the stone from the unfavourable “Blue Zoisite” — which sounded uncomfortably close to “suicide” — to “Tanzanite”, honouring its country of origin. A new covetable gemstone was born.

Tiffany began using Tanzanite in its designs in 1968, becoming the first jeweller in the world to do so, and held exclusive marketing rights for the first ten years. Their 1970s advertising famously described it as “the loveliest blue gemstone discovered in over 2,000 years”, firmly establishing Tanzanite as one of the most sought-after blue gemstones of the modern era.

Its popularity received another boost in 2002, when the International Gem Society added Tanzanite to the December birthstone list alongside turquoise and blue zircon — the first addition since 1912.

Trichroic Properties & Heat Treatment

Tanzanite, the blue variety of the mineral zoisite, is a trichroic gemstone. In simple terms, this means it displays three different colours along three different axes. In its rough, freshly mined state, Tanzanite appears predominantly brown or treacle-coloured due to the dominance of its reddish-brown axis.

Heat treatment removes this axis permanently, revealing the blue and violet tones beneath. Rather than enhancing the colour, heat treatment reduces the stone to a dichroic state, allowing its indigo blues to emerge — much like the accidental discovery following bushfires. Most Tanzanite on the market is heat treated, although natural pinks, greens and browns are occasionally used by jewellers seeking rare, unheated material. Its trichroic nature also means colour varies depending on how the stone is oriented during cutting.

the gemstone of transformation

recovery, assist the immune system, and provide a calming influence during stressful times. Its indigo-violet light is said to encourage creativity, confidence and the release of old patterns.

Once in a generation 

Tanzanite occupies a unique place in the gemstone and jewellery market, closely linked to rarity — the finer the colour, clarity and cut, the higher the value. Its main drawback is its relative softness (Mohs hardness 6.5–7) compared to sapphire and ruby (9) or emerald (7.5–8). While perfectly suited to earrings and pendants, Tanzanite requires care when worn in rings.

Often referred to as the “gemstone of a generation”, Tanzanite may be the only gemstone that appears and disappears within a single lifetime. It is believed the primary deposits will be depleted by the middle of this century. While smaller stones may continue to be recovered from tailings, large flawless gems are becoming increasingly rare.

With its singular colour and finite supply, Tanzanite deserves a place in every jewellery collection — not only for its beauty, but for its rarity, which ensures it will only become more precious with time.