Tanzanite is one of the most important gemstones discovered in the 20th century. It was discovered in 1967 in Tanzania, hence its name coined by Tiffany & Co.
Tanzanite is a rare transparent brownish Green variety of the zoisite species, a calcium aluminium hydroxyl sorosilicate mineral [(Ca2Al3(SiO4)(Si2O7)O(OH)) + (Cr,Sr)], which dramatically changes its appearance to an attractive blue to violet color under low heat treatment. Tanzanite is considered, along with the sapphire, to be the finest blue to violet stone in existence, and its distinct trichroism phenomenon produces a unique appearance.
Fancy color tanzanites are in fact txtremely rare gem-quality zoisites found in all other colors. These are termed tanzanites along with their color prefix, such as green tanzanite.
LEGEND AND LORE
Tanzanite was added in 2002 to the birthstones of December, sharing this title with zircon, turquoise and blue topaz. It is also the gemstone representing the 24th wedding anniversary.
Tanzanite is known to uplift the spirit and open the heart. The blue and purple hues of Tanzanite are associated with generosity and friendship and are helpful in facilitating communication. It is also thought to help one contend with change and solve problems. It is believed to inspire compassion and to encourage calmness and is therefore useful in treating psychological disorders, stress, and nervous tension. Tanzanite helps in overcoming experiences of fear and crises, and in re-building trust.
FANCY COLOR TANZANITE COLORS
Gem-quality colored varieties of zoisite can also be found in all other colors, excluding deep reddish hues, however they are extremely rare. These colors include pink, orange, yellow (‘golden’), green, grey, metallic blue, purple and their combinations. These colors are characterized by low saturation levels (except for orange and very rare purple stones).
CIBJO defines tanzanite as a blue to violet material while the other transparent gem-quality zoisites are defined as tanzanite together with their color prefix (e.g. green tanzanite).
On the other hand, some traders and several gemological institutes limit the use of the name tanzanite to the blue to violet gems only. According to their view, other gem-quality zoisites are defined as fancy colored zoisites (or zoisite with its color prefix – e.g. green zoisite).
Some of the unearthed tanzanite crystals originally possess blue to violet colors without having to undergo any heat treatment. These colors, which have been produced naturally in the depth of the earth, tend to be slightly different from the ones obtained through heat treatment by man – they show a gentle tint of greenish Blue color. In smaller stones, this property is insignificant and all the untreated gems are heated to try to improve the color. However, in larger sizes, such stones may be granted a price premium, and therefore, not all gems would be heated.
Among the available fancy tanzanite colors, pink and purple are considered the most precious and sought after, followed by the chrome green. Vivid oranges and yellows come next.
Most of the color combinations of fancy tanzanite are caused by the trichroism effect of the stone. However, some of the fancy tanzanite gems owe their mixed color appearance to a color zoning within the crystal. These parti-colored zones are usually made of blue and/or green and/or violet colors.
FANCY COLOR TANZANITE SOURCES
All tanzanite is endemic only to the Merelani Hills, near the city of Arusha and Mount Kilimanjaro in Northern Tanzania. This is the world’s only source gem-quality tanzanites. The mines area, only a few square kilometers in size, was divided in 1990 by the Tanzanian government into 4 mining blocks, A, B, C and D. Todays, Block A is licensed and operated by Kilimanjaro Mines Ltd., Blocks B and D are allocated to small-scale miners and Block C is operated by the TanzaniteOne Group.
PHYSICAL PROPERTIES
Variety: Fancy Color Tanzanite
Species/Series: Zoisite
Chemical Composition: Calcium aluminium hydroxyl sorosilicate [(Ca2Al3(SiO4)(Si2O7)O(OH)) + (Cr,Sr)]
Crystal System: Orthorhombic
Color: pink, orange, yellow (‘golden’), green, grey, metallic blue, purple and their combinations
Hardness: 6.0 to 7.0
Refractive Index: 1.691 to 1.70 (±0.005)
Specific Gravity: 3.35 (+0.10/-0.25)
Properties: RI 1.691-1.700 HARDNESS 6-7 SPECIFIC GRAVITY 3.35 SPECIES-ZOISITE OPTIC CHARACTER-DR PHENOMENA-CHATOYANCY(RARE)
Reactions: Reactions
Major Sources: Tanzania
Grading Information: GEM, AAA, AA, A+, A, B
Enhancement Code: Heated to enhance color
Specific Gravity: 3.35
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