Named by Tiffany and Company and exhibiting a brilliant blue hue, Tanzanite is known for its beauty and rarity. In fact, the gem is rarer than diamonds. While a stone with this name is always blue, the shade variation is considerable. It comes in light blue shades as well as in vibrant hues of purplish blue. Jewelry makers use the gem to form earrings, necklaces, and rings.
Discovering a New Gemstone
When it comes to precious gems, people have known and worn the world’s most heavily sought after stones as adornments for hundreds of years. This makes the brilliant blue stone unique because it wasn’t discovered in large enough quantities to sell commercially until the 1960s. The gem is now the second most famous blue stone just after the sapphire.
Tiffany was the first major corporation to sell the stone. When the company marketed the gem initially, it called it “the most beautiful blue stone to be discovered in 2,000 years.” The stone is a mineral named zoisite, and it naturally occurs in a variety of colors including pink, green and yellow in addition to blue. The name “tanzanite” refers to the stones that display color variations that range from blue to violet shades.
To name the gem, the company combined the mineral’s name with its only known commercial mining location, which is in northern Tanzania. The gem’s mines are all within about an 8-square-mile area within the Merelani Hills, which is by the base of Mount Kilimanjaro.
Heating to Enhance the Color
Early on, laboratory testers determined that they could heat blue zoisite to enhance the color of the stone. The gem is blue because it includes small amounts of vanadium. When artisans heat treat blue zoisite to 600 degrees Celsius for at least 30 minutes, the process changes the oxidation state of vanadium, which brings about the blue hue, or if it’s already present, then it makes it appear more vibrant.
While heating the stone decreases its value, the heat treatment procedure for blue zoisite is milder than it is for other gems like sapphires and rubies. These stones are heated to temperatures that range from 1,000 to 1,800 degrees Celsius for several days or even weeks.