Tanzanite is considered by some to be the finest blue stone in existence. Tanzanite, despite its scarcity, has not only gained a remarkable public awareness in a very short space of time, but has become an object of desire worldwide.

Tanzanite is a rare and beautiful transparent indigo-violet gemstone that is found in just one area of Tanzania – and nowhere else. It is by far the most important stone of the zoisite species but a relative newcomer to the gemstone industry, having first been recorded only in 1967. Tanzanite was recognized as a major gemstone when it was launched on the international marketplace, to great success, by the New York jewellers Tiffany & Co. in the late 1960s. In an industry where colour has become a critical factor for jewelry buyers and designers alike, tanzanite plays an important commercial role. For many people, a large blue sapphire would be too expensive to contemplate, yet a large blue tanzanite provides a colourful alternative that is much easier on the pocket.

Purests point out it is barely hard enough to facet at 6.5 and is really just a flash in the pan, only time will tell

Working with zoisite

  • Care needs to be taken when polishing and soldering tanzanite jewelry as heating the stone may damage it or affect the colour. It is also very easy to remove the polish and end up with a dull patch on the crown or girdle.
  • Unfortunately, tanzanite is a relatively soft gemstone that can be brittle and will chip quite easily. It is not suited to everyday wear and as a ring stone would need a protective setting on facet corners and edges. Some traders advise that tanzanite is better kept for earrings, necklaces and pendants

Pricing zoisite
Intially the supply of tanzanite was too unstable for commercial use and market was limited to collectors. In the 1980s there was a surge of material from the Tanzanian mines, which resulted in greater recognition and appreciation of the stone. Supply and demand were high, which kept prices reasonably low and enabled buyers to choose the best quality colours. Natural and political events have occasionally influenced interest and availability, but tanzanite’s value is up and will remain high so long as only one source exists in the world and demand and interest continue to grow. Concerns that the stone will eventually become mined out will no doubt lead to a rise in prices.

The pricing of tanzanite is based on intensity to; colour an intense blue stone will be valued higher than a purple-violet stone. The high price of intense colour has meant that more pale lilac and lavender material is being seen and used – to great effect. The gentler colours of tanzanite only cheaper to buy but offer the designers more a more versatile material to work with; they mix well with other gemstones and are just as popular with buyers.

Treatments and imitations

  • The secret of tanzanite’s success lies in its dramatic colour transformation when heated and its remarkable pleochroic properties. Rough tanzanite crystals display three colours when viewed from different angles (axes), and this pleochroism influences the final colour of the stone after heating. Tanzanites have to be faceted as stones prior to heat treatment, in order that the angle of the table lies in the direction (colour axis) that will produce the best blue. Heating is then performed in a special furnace, where the cut stones are placed in layers of sand or white cement and heated to temperatures of 900-1250°F (480-680°C). Darker and larger stones require higher temperatures for longer periods of time. The brown and honey-yellow tanzanites turn into blue-violet stones, and stones that were originally ink blue become the most expensive intense blue.
  • Tanzanite could be confused with other gemstones, such as amethyst, iolite, sapphire, spinel or synthetic corundum.
  • The popularity of tanzanite has led to the production of very convincing glass imitations and doublets. Either glass stones are given a tanzanite crown or two colourless synthetic spinels are glued together with tanzanite-coloured glue. Other imitation tanzanites on the market go under the names of forsterite, chortanite and cortanite.
  • If you are buying a tanzanite of an expensive colour it is important to have the gemstone tested by a laboratory or use a reputable dealer who will give you a written guarantee and receipt.