Tanzanite is a modern and highly coveted gemstone, celebrated for its rich color that ranges from a deep blue to a vibrant violet. Unlike many gems with ancient histories, tanzanite’s commercial popularity began only in the late 1960s, quickly establishing it as a popular alternative to traditional blue stones. Its intense, unique color spectrum is the primary reason for its appeal.
The Unique Origin and Mineral Identity
Tanzanite was first discovered in 1967 in the Merelani Hills of Northern Tanzania, near the base of Mount Kilimanjaro. The geological conditions required for its formation—including vanadium-rich minerals, heat, and pressure—occurred only once, making this location the world’s sole commercial source for the gem. The stone is scientifically classified as a blue-violet variety of the mineral zoisite.
The luxury jeweler Tiffany & Co. introduced the gem to the world market in 1968. They named it Tanzanite after its country of origin because executives thought the original scientific name, “blue zoisite,” lacked consumer appeal.
Distinctive Visual Properties
Tanzanite’s intense color is unlocked through a precise heat-treatment process. In its rough, natural state, the mineral is typically a brownish-yellow or reddish-brown. Controlled heating to approximately 500°C changes the oxidation state of vanadium within the crystal structure, permanently eliminating the brown component and revealing the desirable blue-violet hues.
Tanzanite exhibits a phenomenon called pleochroism, meaning it displays different colors when viewed along different crystal axes. Before heating, the rough stone is often trichroic, showing three distinct colors. The heat treatment generally reduces this to dichroism, showing the two most prized colors: a saturated blue and a strong violet.
Understanding Tanzanite Value and Rarity
The value of Tanzanite is assessed primarily using the “Four Cs” of gem grading, with color being the most significant factor. The most prized specimens feature a deep, vivid saturation of color that shows an equal balance of blue and violet. Clarity also plays a role, as eye-clean stones—those without visible inclusions—command higher prices than those with internal imperfections.
Larger Tanzanite stones are disproportionately rarer and more valuable per carat than smaller ones, making size a major price determinant. The single-source nature of the gem contributes to its market value. Due to the finite nature of the Merelani deposits, future supply is expected to diminish as the mines deplete.
Practical Guide to Care and Durability
Tanzanite ranks between 6.5 and 7 on the Mohs scale of hardness. It is softer than stones like sapphire or diamond, making it more susceptible to scratching from contact with harder materials. Furthermore, its crystal structure includes a property called perfect cleavage, which means a sharp blow can cause it to crack or split along internal planes.
Tanzanite jewelry should be reserved for occasional wear rather than daily use, especially in rings and bracelets. It is also vulnerable to thermal shock, so sudden temperature changes must be avoided. The safest way to clean the stone is with warm water and a mild, non-detergent soap, using a soft brush. Ultrasonic cleaners and steam cleaning methods should never be used due to the risk of internal fracture.