Tanzanite Is Africa’s Real Blue Diamond
By: Carrie Whitney, Ph.D.
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If rarity boosts a gemstone’s value, tanzanite, which is mined from just one source, could be prized for that fact alone. All the world’s tanzanite is sourced from just 8 square miles (20 square kilometers) near Mount Kilimanjaro in Tanzania. By contrast, diamonds, which are considered rare, are found in more than 30 countries and on multiple continents.
Recognizable for its vibrant blue-violet color, tanzanite owes its place among today’s favorite gemstones not only to its recent discovery, but also to a modern publicity campaign that catapulted the gem to fame.
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In gemology, stones are divided into species and variety, according to Brenda Harwick, Gemological Institute of America (GIA) senior manager of gemology instruction, and tanzanite is a variety of the species zoisite. It is considered a gemstone, which means it has a specific chemical composition, is natural and is inorganic. In the case of tanzanite, that composition includes calcium, aluminum, silica oxide and hydroxide. In other words, it’s a calcium aluminum hydroxy silicate.
What’s important anywhere but chemistry class, is that tanzanite boasts two important gemstone qualities: beauty and rarity. One of the prize features of a gemstone is that it cannot be found everywhere on Earth, Harwick explains. It requires certain geological events to form.
“Nature is interesting, and it really is unique when gemstones form because it does involve having the right temperature, the right pressure and the right chemical composition,” she says. “And that is part of its allure.”
On the Mohs Hardness Scale, tanzanite falls in the 6 to 7 range, which makes it easier to scratch than diamonds (10), rubies and sapphires (9), or even quartz (7). With its softer nature and fair-to-poor toughness ranking, tanzanite is one of the more delicate gemstones. It’s also sensitive to thermal shock — or sudden temperature changes.
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Tanzanite is found in one place on Earth — Tanzania. Although it’s not as expensive as a diamond, tanzanite is much rarer. In fact, some estimates have tanzanite at 1,000 times rarer than diamonds.
It may be hundreds of millions of years old, but the gem was first brought to the attention of humans in 1967, according to the website for Cape Town-New York jeweler Shimansky. Legend says tanzanite was first discovered either by a Masai tribesman (the Masai are an ethnic group living in northern, central and southern Kenya and northern Tanzania) who first noticed the bright blue crystals and contacted Manuel de Souza, an Indian tailor and prospector, or else it was found by de Souza himself.
Either way, with hope that the colorful deposit was sapphire, de Souza made a mining claim to the area. Although zoisite, the species of which tanzanite is a variety, was known at the time, it was typically translucent, opaque, green and used for carving jewelry, according to Harwick. Tanzanite’s brilliant color was an exciting find.
The late Harry Platt, former chairman of Tiffany & Co., is credited with introducing the blue gemstone to the world. According to The New York Times, Platt spotted it while visiting a lapidary in Europe and not only gained the rights to sell the stone, but also got to name it, which he did in honor of the country where it was discovered. More than five decades later, the Mount Kilimanjaro source near Arusha, Tanzania, is still the only place in the world to source the gem.
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Tanzanite is known and appreciated for its pure blue or blue-violet color, which is similar to sapphire. It is color, after all, that sells colored stones, Harwick says. So better stones have more intense color and will weigh 5 carats or more. The bigger the stone, the more intense the color, the better the value.
Interestingly, most tanzanite does not display its vibrant color when mined. As much as 95 percent of the gems mined are heat-treated to achieve the blue color. Most tanzanite comes out of the Earth with a brownish hue. Once heated to a brilliant blue, tanzanite’s color is stable, so buyers do not need to worry that it will fade.
Depending on how tanzanite is cut, the color may start to lean toward a gray or purple hue, which can lower its value. Additional varieties of zoisite include thulite (pink) and anyolite (red/ruby), and it can also show up as other colors like greenish or yellow.
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Although tanzanite is rarer than both diamonds and sapphire, it commands a lower price on the market. One reason might be the durability factor; tanzanite is only “reasonably durable,” while sapphires are second only to diamonds in durability, according to Angara.com. While a sapphire might range from $800 to $1,200 per carat, tanzanite can be had for just $300 to $425 per carat, making it a cost-effective substitute for sapphire depending on the application.
To put both of these gems in perspective, diamonds start at around $3,080 per carat and can increase in value significantly from there. Of course, value changes with supply and demand, so prices fluctuate.
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Like many gems, tanzanite does not have any specific industrial value, but it has an important place in the jewelry industry. There aren’t many blue stones, especially with such vibrant color, and tanzanite does not have a synthetic counterpart.
Some people consider gemstones to have healing or spiritual purpose. Certainly, ancient peoples had specific beliefs about them and uses for them. But we can’t delve into the history of tanzanite because its discovery is so recent.
When it burst on the jewelry scene in 1968, tanzanite changed the direction of Tiffany & Co.’s style from “simple gold jewelry to colorful designs with large stones,” Melanie Abrams wrote for The New York Times in 2018. Because of its less durable nature, tanzanite works well in special occasion jewelry or items that like necklaces and earrings.
People with December birthdays had something extra to celebrate in 2002 – tanzanite was added to the list of the month’s birthstones, joining zircon and turquoise, also blue, but admittedly less brilliant.
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