History and General Information -Natural Tanzanite Gemstone

Tanzanite Gemstone is one of the most recently discovered gemstones and is coveted by specialists as the gemstone of the 20th century. According to tanzanite history, the gemstone’s discovery is fairly interesting. The belief is that millions of years ago, these crystal deposits were formed during the metamorphic process of schists, gneisses and quartzites. These processes were completely hidden to the human eye. Tanzanites are also called as the December Birthstone.

Then a more recent narrative suggests that in 1967, Ali Juuyawatu, a local Maasai tribesman, found a piece of translucent crystal at a ridge near Merarani and at the foothills of Mount Kilimanjaro. Fascinated by its blue-violet hue, he shared his find with Manuel D'Souza, a tailor by profession and prospector by passion, who was looking for rubies in the region. Realising that the mineral was not olivine (peridot) the stones found their way across the continent to New York at Saks.

The Gemological Institute of America identified the samples as a variety of the mineral zoisite and similar observations were made by other leading museums and universities. However, the first person to correctly identify the stone was a Tanzanian government geologist in Dodoma. Saks got two of the samples facetted and showed them to Henry Platt of Tiffany and Co. who was impressed with the beauty of the gem and coined it ‘tanzanite’, in honor of the country of its origin, thereby making the gemstone more marketable to the public.

Compostion of Tanzanite Gemstone

Tanzanite gemstone is a calcium aluminium silicate (Ca2 (Al OH) Al 2 {SiO4}3). Its specific gravity is 3.35 and its refractive index ranges between 1691 and 1.700. The gem’s hardness on the Mohs scale is 6.

Varieties

Zoisite mineral is found in many colors like blue to violet, green, brown, pink, yellow, gray or colorless. It has three gemstone varieties, i.e tanzanite, thulite and anyolite.

Tanzanite

Tanzanite is a blue variety of the mineral zoisite that occurs either in crystal or massive forms.

Thulite

Thulite is the opaque and massive pink variety of zoisite. It is sometimes referred to as rosaline and is colored by manganese. It is extremely rare and apart from being a collector gem, thulite is used as a carving material in the manufacture of jewelry and ornamental products.

Anyolite

Anyolite is the green variety of zoisite. Also known as ruby in zoisite or Tanganyika artstone, anyolite is a metamorphic rock of inter grown green zoisite, black hornblende and ruby. It is used commonly as a material for sculptures and decorative objects.

Physical Properties

Tanzanite Color

What makes genuine natural tanzanite gemstone so special and unique is its color spectrum that runs from ultramarine blue to light violet-blue, unlike any other gemstone. The most appreciated color of this gemstone is a blue surrounded by a delicate hint of purple, which has a particularly wonderful effect in larger sized tanzanites.

Tanzanite gemstone is also distinguishable for its remarkably strong trichroism, which means that in its rough form the gem radiates three different colors namely blue, violet and burgundy, depending on the crystal orientation. The trichroic property makes the beautiful gem more special. Larger stones tend to exhibit more intense color, fire and brilliance. A richly colored genuine tanzanite crystal typically commands a higher price.

Cut

A tanzanite crystals cut is intrinsic to the value and price that the stone can command in the international market. A very good faceted cut ensures that the stone’s facets reflect light proportionately and exudes maximum brilliance. If cut too deep or too shallow, a tanzanite's radiance will deflect through the sides from the bottom of the stone, affecting its brilliance. Today, the Indian city of Jaipur is the world largest tanzanite gem stone cutting center and it accounts for one-third of Jaipur’s annual gem exports. The image shown here are a pair of trillion cut tanzanites.

Carat

Due to the rarity of the gem and the precision required in cutting tanzanite gemstones, larger gems command a premium price. A tanzanite gemstone of 2-3 carat, for example, will fetch an exorbitant price in the market.

Clarity

Tanzanite gemstone exhibits clarity ranging from completely clean to clean or with slight inclusions (that can only be viewed under magnification) to heavily included stones. The stone, that is flawless or with minor inclusions, is considered perfect to the unaided eye. The more flawless the tanzanite gem stone, the more valuable it is.

Price and Cost of Natural Tanzanite Gemstone

As in most other gemstones, tanzanite prices depend largely on color, cut, clarity and of course carat. The most prized color for tanzanite crystals is either sapphire blue or the intense violet-blue. The paler shade of bluish purple is also popular and quite affordable. As the cut of the gem plays a very important role in a tanzanite’s price, at times the size of the stone is compromised to get that perfect deep blue color. Hence, in order to cope up with the large demand for this precious gemstone, the market seems to be flooded with treated and synthetic tanzanites.

As per a recent price index, wholesale prices for top fine quality tanzanite gems were about US $500 per carat in late 2007 and retail prices for high grade tanzanite ranged from US $500 to $1200 per carat. Further, when buying a tanzanite it is always advisable to purchase a certified stone from a reputed gemological laboratory.

Though tanzanite jewelry has not become extremely popular, some designers are beginning to use the gemstone to make tanzanite rings, tanzanite earrings and even tanzanite engagement rings. Tanzanite in white gold is another setting that the modern designers have tried. Due to its color, the gemstone pairs well with diamonds and a tanzanite and diamond gold ring can make an interesting and unique anniversary gift.

Markets and Producers

The world's only known source of natural tanzanite rough occurs beneath the grasslands at the foothills of Mount Kilimanjaro in northern Tanzania. Nearly two decades ago, the Tanzanian government demarcated the tanzanite mining area into four blocks - A, B, C and D, measuring approximately 5km by 2km in total where tanzanite is mined almost exclusively.  Expert geologists and collectors maintain that the chance of tanzanite occurring elsewhere in the world is one in a million.

Treatments done on Natural Tanzanites

Most natural tanzanites in the market today are heat-treated to enhance their color, thereby subduing their trichroism. For example, on treatment, an original subdued brownish tanzanite is heated to transform it in to an attractive blue-violet or deep blue. The price versus value equation changes automatically. While gemmological tests help differentiate a treated gem from an untreated one, treatment is an accepted practice in the market. The trader however, must reveal the fact that the tanzanite has been treated at the point of sale.

Simulants

Gem stones that are confused with tanzanite are iolite, inferior quality blue sapphire, blue spinel and synthetic tanzanite. A periwinkle blue or lavender colored cubic zirconia has also recently come into general use as a tanzanite simulant.

Synthetic Tanzanites

Lab created simulant of tanzanite is called tanzanique. It closely mimics the color of natural tanzanite however it does not display the same pleochroism. While tanzanite is the variety of mineral zoisite, tanzanique is fosterite.

Interesting Trivia and other fact

Unlike other gems, tanzanite is a fine quality gem and has managed to stand its own in the world gem market in spite of the fact that it is a close substitute for the blue sapphire. 

In Auugust 2005, the largest tanzanite crystal was found in the C-Block mine. The crystal weighs 16,839 carats (3.4 kg) and measures 22 cm by 8 cm by 7 cm

Tanzanite Gemstone is lucky for people born in the month of December and hence it is also called as the December Birthstone along with blue turquoise gemstone.

Reference

1) Webster
2) Gemmology by Peter G.Read
3) Handbook of Gem Identification -   Richard  T.Liddicoat, jr
4) Gems and Crystals - From the American  Museum of Natural History - Anna S.Sofianides  and George E.Harlow.