Tanzanite

The name “tanzanite” is used for a color variety of zoisite that ranges from blue, through violet, to violetish purple.

Tanzanite may be a relative newcomer to the world of colored stones, but it was one of the most exciting gem discoveries of the 20th century. Blue stones emerging from Tanzania were identified as the mineral zoisite in 1962. In 1967 prospectors locate the primary source for this lovely gem. Tiffany became one of the main distributors and in the sequent year, Tanzanite was the protagonist of sensational marketing campaign in USA.

Tanzanite gems

Kat Florence – Arunashi’s earrings – Nigaam ring

Sarah Jessica Parker wearing Kat Florence’s tanzanite necklace

5 Facts

 

  1. Tanzanite was discovered only 54 years ago.
  2. According to an old Masai affinity with blue color, tanzanite is considered the gem of New Born and New life, good luck and prosperity.
  3. The gem worn by Kate Winslet in Titanic to evoke the “Heart of the Ocean” necklace was a Tanzanite!
  4. The conditions responsible for creating tanzanite were so unique that the chance of finding tanzanite in another part of the world are less than a million to one. Geologists attested that tanzanite source will be exhausted in only 10-20 years.
  5. Tanzanite is the 24th wedding anniversary gem and the December Birthstone

Rough, Cut, Carat Weight & Optical properties

 

Tanzanite pleochroism

As the name suggests, tanzanite is sourced in Tanzania, in fact the Merelani Hills (in the northern country) is the only place on earth where this extraordinary gem is mined comercially.

Tanzanite’s appearance is influenced greatly by its pleochroism, which is the ability of a gemstone to show different colors when viewed in different crystal directions. Tanzanite shows three different colors when viewed from different directions: red-violet, deep blue, and yellow green.

The pleochroism in natural tanzanite is so strong that it is visible by just turning the stone and viewing it through different directions without the aid of a dichroscope.
As you can read in the post dedicated to tanzanite’s cut, the exact face-up color depends on the inherent color of the original rough, its size, the pleochroic colors the cutter favors when they orient the fashioned stone, and the light the finished gem is viewed under. Cool lighting – like daylight equivalent fluorescent – will emphasize tanzanite’s blue, while warm lighting – like incandescent – will make it appear more violet-to-purple.

The cut is particularly important for Tanzanites because of its pleochroism in fact the cut influences drastically the gem overall face-up color.
The cutter might choose if enhance the violet-to-purple color saving rough weight or emphasize the violetish blue color faceting a smaller gem. A balance of the two considerations is the most desirable result.

Tanzanites are available in many different shapes and faceted cuts, the most common are oval and cushion style. Tanzanite color might be deeper and more velvety in stones above 5 carat and cushion cut enhance even more the gem optical qualities. 

A large, clean rough Tanzanite in natural and rich violet-blue color is becoming extremely rare, so larger fine gems are rapidly rising in price and decreasing in availability.

Clarity & Color

 

Tanzanite color chart

For Tanzanite color is the most predominant factor by the way eye visible inclusions can decrease its value.
Tanzanite has an attractive vitreous luster and is often of high clarity.
The best quality tanzanite is “clean” and free of visible inclusions of any kind that can be viewed only by a jewelers loupe.
Also important to underline that some inclusions as fractures might pose durability problems. Therefore these affect drastically the gem value.

Just like other colored gemstones, vivid strongly-colored tanzanites are highly sought after. The mineral zoisite naturally occurs in a wide range of colors that include colorless, gray, yellow, brown, pink, green, blue, and violet. Tanzanite gains its distinctive purplish blue colour from the trace elements of vanadium and chromium present within its structure.
Tanzanite rarely appears to be pure blue, and almost always displays visible violet tones.

When graded by gemologists, a tanzanites color is always stated as a combination of blue and violet. A tanzanite which displays more than fifty percent blue in white light will be graded as “violetish Blue/vB “. Stones with a predominance of violet will receive the grade “blueish Violet/bV “.

The depth of color ranges from pale to deep hues. The deeper the color, the rarer the tanzanite. Larger stones are frequently darker and it unusual to find an intensely saturated stone under 5 carat’s in weight. There is no price difference between a vB or bV stone – however lighter stones are more commonly found than darker, more saturated stones which command a price premium. Tanzanite will appear more violet when viewed under yellow lighting.

Deep saturated violet blue or blue violet are the most valuable tanzanite colors.

Tips

 

Tanzanite certificate

The vast majority of tanzanite on the market today is heat-treated to enhance its colour and marketability. The treatment is permanent and stable in the time. Gemological laboratories cannot test for heat treatment as it generally occurs naturally in the Earth as well and there is no effect on price.
To date, tanzanite has not been created synthetically. The most common imitation is blue-violet glass, which is easy to identify for a gemologist.

Dalila Daffara