Exploring the Mysteries of Tanzanite Gemstones
==================================================
In the heart of Tanzania, near Mount Kilimanjaro, a unique gemstone was discovered in 1967 that would captivate the world. This purplish blue gemstone, known as tanzanite, is a rare variety of zoisite, a species of gemstones with the same chemical composition.
The name "tanzanite" was given by Tiffany & Co., who rebranded the stone from “blue zoisite” to honor its Tanzanian origin and help popularize it in the jewelry market. Tiffany held exclusive rights to market the gem in the 1970s, contributing to its high value and fame.
Tanzanite is found exclusively in a very small geographic area, roughly a 4 km strip, making it one of the rarest gemstones in the world. Geologically, it formed about 585 million years ago due to tectonic activity in the region. Current projections suggest the mines will continue to produce gem-quality material at the same rate for another 23 years, after which the supply is expected to deplete.
In terms of value, tanzanite ranks as the second most valuable blue gemstone after sapphire. Its value depends on factors including color saturation (deep blue-violet hues command higher prices), clarity, cut, and size—the larger stones being disproportionately rarer and more expensive per carat. Heat treatment is commonly used to enhance tanzanite’s color from a raw brownish state to the vibrant blue-violet prized in jewelry, which is broadly accepted if properly disclosed.
Tanzanite measures between 6 to 7 on the Mohs scale and is more liable to scratches and damage, making it less suitable for everyday wear as a ring. On average, tanzanite prices range from £225 to £1,100 per carat, depending on size, color, and treatments.
When purchasing tanzanite, it is advisable to use a 10x loupe to examine the cut, clarity, and any presence of chips or cracks, and to compare a number of stones to gauge the hue and saturation of color.
Tanzanite can be found in the Gem-A Gemstone & Mineral Collection, along with other specimens such as sugilite, stibnite, and decorative fossils. Synthetic forsterite can be a convincing simulant of tanzanite but can be differentiated by its vivid blue and purple pleochroic colors. Tanzanite shows strong pleochroism, an optical property, which is visible by just turning the stone and viewing it through different directions without the aid of a dichroscope.
In 2002, tanzanite became adopted as a new birthstone for December by the American Gem Trade Association (AGTA). The largest tanzanite ever sold at auction is the 423.56 Namunyak Tanzanite, which was set into an 18-carat white gold necklace and fetched over $300,000 USD at a charity sale in 2016.
Tanzanite is not currently synthetically produced. The Gem-A Gemmology Foundation course and various Short Courses and Workshops are available for those interested in starting their gemmology journey. Tanzanite crystals are usually prismatic and well-formed, with crystals over 50 carats being rare and sold to collectors rather than being cut.
The largest piece of tanzanite rough ever reported was found in 2005 by TanzaniteOne Mining Ltd, weighing 16,839 carats (7.43lbs or 3.37kg). Providing tanzanite has not been heat-treated, it will show three pleochroic colours: red-violet, deep blue, and a greenish yellow. However, if heated above circa 400°C to 500°C, the greenish yellow colour is removed or substantially reduced and the bluish colour deepens.
In summary, tanzanite’s recent discovery, limited geographic source, vivid color, and finite supply underpin its rarity, availability, and value in the gemstone market.
- The Gem-A Gemmology Foundation course offers opportunities for individuals to start their gemmology journey, including learning about tanzanite, a gemstone found exclusively in a small area near Mount Kilimanjaro in Tanzania.
- Tanzanite's value is influenced by factors such as color saturation, clarity, cut, and size, with deep blue-violet hues commanding higher prices due to their rarity.
- Tanzanite can be found in publications, exhibitions, and collections, such as the Gem-A Gemstone & Mineral Collection, alongside other rare specimens like sugilite, stibnite, and decorative fossils.
- Tanzanite shows strong pleochroism, an optical property that is visible by turning the stone and viewing it through different directions without the aid of a dichroscope.
- In terms of finance, tanzanite prices range from £225 to £1,100 per carat, depending on size, color, and treatments. However, larger stones are disproportionately rarer and more expensive per carat.
- The largest tanzanite ever sold at auction is the 423.56 Namunyak Tanzanite, which was set into an 18-carat white gold necklace and fetched over $300,000 USD at a charity sale in 2016.
- Tanzanite is not only a prized gemstone in the science of gemmology but also in jewelry, lifestyle, entertainment, and sports, with its distinctive color and rarity captivating the world since its discovery in 1967.
