Distinguishing Features
Tanzanite is pleochroic, showing three different colours when viewed from different directions.
Fine tanzanite’s strong pleochroism and intense violet-to-blue face-up colours help identify the gem and provide a large part of its value.
The Most Desirable Picks
Colour:
The gem is famed for intensely saturated, pure blue or violetish blue stones. Each fashioned gemstone usually displays a mix of blue and violet hues, depending on the viewing angle. In exceptional tanzanites, the colour is an intense violetish blue with red flashes of pleochroic colour coming from within the stone. Lighter toned pastel hues are more plentiful and affordable than vivid colours and have a subtle appeal.
Note: Most blue tanzanites for sale today owe their colour to heat treatment. Untreated, tanzanite is typically brownish.
Clarity:
Much of the tanzanite sold for jewellery has inclusions that can be seen only under magnification. Eye-visible inclusions decrease the value of tanzanite, particularly in lighter coloured stones, where they're more visible against the gem's body colour. Any inclusions that might pose durability problems—such as fractures— would lower the tanzanite value greatly.
Cut:
Tanzanite is available in various shapes, but cushions, trillions, and oval cuts are most common. Cutting orientation can emphasize which colours are seen through the gem's crown. Cutting to display a gem's violet colour face up usually retains more carat weight from the rough than fashioning it to show a predominantly blue hue.
The toughness of tanzanite is fairly poor, and its hardness is 6-7 on the Mohs hardness scale. Jewellery manufacturers must be thoughtful when setting tanzanite in daily jewellery, and the wearer needs to be more careful.
Carat Weight:
Tanzanite is available as fine, larger pieces with strong colour or lighter material cut to standard sizes in mass-market jewellery. Gems must be above 5-cts. In size to have deep, fine colour. Tanzanite colour is less saturated in smaller sizes.
Origins
The hills of Merelani in northern Tanzania.
Significant Pieces
Tiffany & company named tanzanites after the country it came from and was the first jeweller to use the gem in its designs just one year after their discovery. The company launched tanzanite onto the world stage with an unprecedented marketing campaign in 1968.
In one advertisement, a selection of tanzanite rings are pictured against a backdrop of grazing zebras, along with the message: "From the foothills of Mt Kilimanjaro comes tanzanite, the loveliest blue gemstone discovered in over 2,000 years. Tanzanite can now be found in significant quantities in only two places in the world. In Tanzania. And Tiffany's." Tanzanite is said to be 1,000 times rarer than diamonds because it's only mined within a few square miles in Tanzania. And, unlike diamonds, tanzanite can be certified to be conflict-free.
Formation
Tanzanite was formed over 585 million years ago, created by massive tectonic plate activity and intense heat in the area that would later become Mount Kilimanjaro. Tanzanite deposits are located within a relatively complex geological environment and are found in “sausage-shaped” boudin structures, typically located in the hinges of isoclinal folds (folds dipping in the same direction).
Reference: Tanzanite One. (2022, 06 07). Tanzanite Mining. Retrieved from Tanzanite One: https://www.tanzaniteone.com/tanzanite-mining
Stability
Care and Cleaning
Avoid using hot water or scrubbing your jewellery with harsh or abrasive chemicals like chlorine or bleach, and avoid using ammonia-based cleaners.