The Tanzanite
A thousand times rarer than diamonds, revered for its kaleidoscopic blue-violet hues.
Overview
Tanzanite is one of the most intriguing and popular blue gemstones available today. Belonging to the zoisite mineral group, this rare gem wasn't discovered until 1967 in the foothills of Mount Kilimanjaro in Tanzania.
Legend says the foothills were set ablaze by lightning, and in the aftermath, Masai herders found violetish-blue crystals amidst the ashes. Found only in a tiny seven-square-kilometer area, geologists believe the events that led to its formation 585 million years ago were so exceptional that finding tanzanite anywhere else is practically impossible. Today, it is regarded as the second most sought-after blue gem after sapphire.
Symbolism
Tanzanite is highly pleochroic, appearing in different colors when viewed from different angles. This fluidity is believed to facilitate higher consciousness and convert negative energy into positive, constructive thoughts.
Known as the modern birthstone for December and the stone for 24th wedding anniversaries, it is also highly prized among the Maasai tribes, where it is presented to wives to celebrate the birth of a child and to bless the newborn with good luck and prosperity.
Physical Properties & Quality
Hardness & Strength
Tanzanite exhibits a hardness of 6 to 7 on the Mohs scale. While it can be used in all types of jewelry, it features perfect cleavage, making it susceptible to chipping from sharp blows or rapid temperature changes. Proper settings and careful wear are essential.
Treatment
Naturally occurring zoisite comes in yellow, brown, and green. A mild heat treatment (600°C for ~30 minutes) is administered to safely transform these crystals into the vivid blue-violet tanzanite we love. This enhancement is stable and will not fade under standard light.
Color & Clarity
Color is crucial to its value. Deep, highly saturated blue is the most prized, followed by bluish-purple. Because tanzanites are typically transparent with an attractive vitreous luster, they should ideally be "eye-clean." Any visible inclusions will result in a drop in value.
Cut & Carat Weight
Because of its pleochroism, cutting is critical to showcase the best color on the top axis. Oval and cushion cuts are the most common. The finest, most saturated colors are usually seen in larger carat weights, making large, flawless stones exceptionally valuable.
Tanzanite Grading System
Top 1%
Comprising the top 1% of exceptionally rare tanzanites, these exhibit flawless brilliance (eye-clean) and are distinguished by a rich, deeply saturated violetish-blue color.
Top 10%
Representing the top 10% of natural tanzanites, these gemstones are also completely “eye-clean” and display an intense blue color with a stunning purplish tint.
Top 33%
In terms of quality, this category includes the top 33% of available tanzanites. They are medium violet-blue in color and feature slight inclusions.
Top 75%
Light violet-blue in color, this entry-level grade includes the top 75% of available tanzanites that have slight to moderate visible inclusions.
Tanzanite Care Instructions
Because tanzanite is softer than many gems and exhibits perfect cleavage, it should be protected from hard blows and rough usage. Good maintenance will ensure it never loses its magnificent sparkle:
- No Ultrasonic Cleaning: Never use ultrasonic or steam cleaners. High-frequency vibrations and extreme heat will damage the gem and can cause it to crack.
- Avoid Extreme Temps: Store your tanzanite jewelry away from direct sunlight, extreme heat, or sudden changes in temperature.
- Gentle Washing: Use warm water, mild soap, and a soft brush to clean your jewelry. Air dry or towel dry (do not use a blow-dryer).
- Avoid Chemicals: As with all gems, keep your tanzanite jewelry away from acids, cosmetics, and harsh household chemicals.
- Store Separately: A compartmentalized jewelry box or a fabric-lined pouch will keep it apart from harder stones (like diamonds), preventing friction and scratches.