Tanzanite, the December birthstone, is a gemstone of extraordinary beauty and rarity. Discovered in the 20th century, it has captivated collectors, jewelers, and gemstone enthusiasts with its deep blue to violet hues and its unique geological history. While it may not have the centuries-old legacy of some other birthstones, tanzanite’s story is no less compelling. This article explores the history of tanzanite, its geological formation and sources, its physical and optical properties, its cultural and metaphysical associations, and its care and preservation. With its limited geographic origin and vibrant color, tanzanite remains a rare and treasured gemstone.
History and Lore
Tanzanite is a relatively modern gemstone, with its discovery and rise to popularity occurring in the mid-20th century. The gem was first identified as the mineral zoisite in 1962. It wasn’t until 1967 that tanzanite was officially discovered as a distinct variety of zoisite, located in the Merelani Hills of northern Tanzania. The discovery was made by a Tanzanian miner who noticed the vivid blue crystals among the local rock formations. The gem was eventually named tanzanite in honor of its country of origin.
Tanzanite quickly gained international attention, largely due to the efforts of Tiffany & Co., who recognized its potential and launched a major marketing campaign in 1968. This campaign helped establish tanzanite as a premier colored gemstone and contributed to its growing popularity. Today, tanzanite is not only a December birthstone but also the gemstone for the 24th wedding anniversary, a testament to its enduring appeal.
The gemstone’s rarity and beauty have made it a symbol of exclusivity and elegance. Unlike many other gemstones that have been known for centuries, tanzanite’s modern origin gives it a unique place in the world of colored stones. It is often described as having a “velvety” appearance, with deep and saturated colors that range from pure blue to violet, with the blue being the most valuable.
The discovery of tanzanite also marked a significant moment in the history of gemstone exploration. Prior to its discovery, the only blue gemstones of significant value were sapphires and, to a lesser extent, blue topaz. Tanzanite’s emergence introduced a new option that combined rarity, beauty, and marketability.
Geological Formation and Sources
Tanzanite is a variety of the mineral zoisite, a calcium aluminum silicate with the chemical formula Ca₂Al₃(SiO₄)(Si₂O₇)O(OH). What distinguishes tanzanite from other zoisite varieties is its striking blue to violet color, which is caused by trace amounts of vanadium. This trace element, when present in the crystal lattice of zoisite, alters the way light is absorbed and reflected, resulting in the gem’s characteristic deep blue color.
Tanzanite is formed under specific geological conditions that are found only in a very limited area of the world. The only commercially viable source of tanzanite is the Merelani Hills in northern Tanzania, a region known for its unique geology. These hills are located near the snow-capped slopes of Mount Kilimanjaro, one of the highest peaks in Africa. The area is characterized by rugged terrain, grass-covered hillsides, and rocky soil.
The tanzanite deposits in the Merelani Hills are located deep underground, with mines extending over 100 meters (more than 300 feet) below the surface. The extraction process involves large-scale mechanized mining operations, where thousands of workers recover the gemstones from the earth. The exact geological processes that led to the formation of tanzanite in this region are not fully understood, but it is believed to have occurred through a combination of high-pressure and high-temperature conditions associated with the collision of tectonic plates.
The rarity of tanzanite is partly due to the limited geographic distribution of its source. While other gemstones like sapphires and rubies can be found in multiple countries around the world, tanzanite is unique to Tanzania. This exclusivity has made tanzanite one of the most sought-after colored gemstones in the world.
Gemological Properties
Tanzanite has several notable gemological properties that make it a desirable gemstone for both collectors and jewelry designers. Its chemical composition and crystal structure contribute to its optical properties, while its hardness and durability determine how it is best used in jewelry.
Chemical Composition and Crystal Structure
Tanzanite is a variety of zoisite, with the chemical formula Ca₂Al₃(SiO₄)(Si₂O₇)O(OH). It is a member of the epidote group of minerals, which includes other gemstones like thulite and clinozoisite. Tanzanite is typically found in prismatic to tabular crystals, and its crystal system is monoclinic.
The blue to violet color of tanzanite is caused by the presence of vanadium impurities in the crystal lattice. When exposed to heat, tanzanite can undergo color changes, which is why many tanzanite gemstones are heat-treated to enhance their color. This treatment is a standard practice in the gem industry and is considered stable and permanent.
Hardness and Durability
On the Mohs scale of hardness, tanzanite ranks between 6 and 6.5. This is relatively soft compared to other colored gemstones like sapphires (9) or rubies (9), but it is harder than many other gems like peridots (6.5–7) and topaz (8). While tanzanite is not as hard as some of the other birthstones, it is still durable enough for use in jewelry, provided it is handled with care.
Tanzanite is also sensitive to heat and light. Prolonged exposure to strong light can cause some tanzanite gemstones to fade or revert to their original color, which is typically a light brown or yellow. This is why it is recommended to store tanzanite jewelry in a dark place when not in use.
Tanzanite is also relatively stable when exposed to common chemicals, making it safe for use in everyday jewelry. However, it is still advisable to avoid exposing tanzanite to harsh chemicals or extreme temperatures.
Optical Properties
Tanzanite is known for its excellent refractive properties, which contribute to its brilliance and luster. It has a refractive index of approximately 1.69 to 1.70, which is lower than that of diamonds (2.42) but higher than that of many other colored gemstones. This gives tanzanite a moderate level of brilliance and sparkle.
One of the most unique optical properties of tanzanite is its pleochroism, the ability to display different colors when viewed from different angles. Tanzanite can exhibit blue, violet, and even brownish hues depending on the angle of observation. This effect is one of the reasons why tanzanite is so visually striking and is a key factor in its appeal.
Symbolism and Metaphysical Beliefs
While tanzanite is a relatively modern gemstone, it has quickly developed its own set of meanings and associations. Like many other birthstones, tanzanite is believed to have various metaphysical properties and symbolic meanings.
In modern times, tanzanite is often associated with transformation and healing. It is believed to help individuals navigate emotional and spiritual changes, making it a popular choice for those undergoing significant life transitions. The gemstone is also associated with intuition and spiritual awareness, and it is said to enhance one’s ability to understand and interpret their inner self.
Tanzanite is also considered a stone of compassion and understanding. It is believed to promote empathy and encourage individuals to see the world from other perspectives. This makes it a valuable gemstone for those in roles that require strong interpersonal skills, such as therapists, counselors, and mediators.
In the realm of metaphysical healing, tanzanite is said to have a calming effect on the mind and body. It is believed to help reduce stress and anxiety and to promote a sense of inner peace and tranquility. Some practitioners of crystal healing also use tanzanite to support the physical body, particularly in relation to the throat and heart chakras.
Tanzanite is also associated with the concept of time and change. Given that it is a December birthstone, it is often used in jewelry and ceremonies related to the end of one year and the beginning of another. This makes it a popular choice for those looking to mark significant milestones or to celebrate the passage of time.
Care and Cleaning
Because of its relatively low hardness and sensitivity to light, tanzanite requires careful handling and proper cleaning to maintain its beauty and longevity.
Tanzanite should be cleaned using a soft brush and mild soap in warm water. Ultrasonic and steam cleaners are generally not recommended for tanzanite, as they can cause the gemstone to lose its color or become damaged over time. It is also advisable to avoid exposing tanzanite to harsh chemicals or abrasive materials.
When not in use, tanzanite should be stored in a dark place to prevent fading. It is best to keep tanzanite jewelry in a soft pouch or a lined jewelry box, away from direct sunlight or artificial light sources. This will help preserve the gemstone’s color and prevent any potential damage.
Tanzanite is not suitable for all types of jewelry use, particularly in settings where it will be subjected to frequent impact or abrasion. While it is durable enough for use in rings, necklaces, and earrings, it is best to avoid wearing tanzanite jewelry during activities that involve heavy physical contact or exposure to harsh environments.
Conclusion
Tanzanite is a rare and beautiful gemstone that holds a special place in the world of birthstones. With its deep blue to violet color and its unique geological origin, it is a gemstone that stands out for both its visual appeal and its rarity. Discovered in the Merelani Hills of northern Tanzania, tanzanite quickly gained international recognition and became a favorite among collectors and jewelers alike.
The gemstone’s history is marked by its modern discovery and its rapid rise to prominence in the gem industry. Its physical properties, including its chemical composition, hardness, and optical characteristics, contribute to its enduring appeal. Tanzanite’s metaphysical properties and symbolic meanings further enhance its value, making it a gemstone that resonates with many different people.
Despite its relatively recent introduction, tanzanite has become a beloved December birthstone, and its continued popularity is a testament to its beauty and significance. Whether used in jewelry, as a symbol of transformation and healing, or simply admired for its natural beauty, tanzanite remains a gemstone that is as rare as it is remarkable.