What color is natural tanzanite?

Gem lovers are well aware of the beautiful blue gemstone Tanzanite. But not everyone knows that tanzanite is a type of the mineral zoisite. Zoisite is a silicate of complex composition with the chemical formula Ca₂Al₃(SiO₄)(And₂O₇)O(OH). Tanzanite is a single-crystalline variety of yellow and brown-gray zoisite with an admixture of vanadium and chromium, the annealing of which at a temperature of 400-500 °C produces beautiful violet-blue crystals with a pronounced and unique blue-crimson pleochroism. The discovery, that is, the fundamental discovery of tanzanite, occurred in January 1968 quite by accident in the town of Keteto in the Arusha region, well known to all stone lovers, at the foot of the equally famous Merelani hills on one of the spurs of Africa’s most famous mountain Kilimanjaro. In these places, until 1967, several For decades, other precious stones have been mined: aniolite (meaning “green” in Swahili – a mixture of green zoisite and ruby), tourmalines, rubies, tsavorites, aquamarines and much more. In January 1967, a miner named Ndugu Jumanne Ngoma (which translates from Swahili as “the man who plays music on Tuesdays”…!? – remember Jumanji?) was walking across the savannah to visit his relatives in the village of Kiteto. The world’s first crystals of blue zoisite, later called tanzanite, were picked up by him in the dust right on the ground. The largest crystal from the 5 kilograms of precious stones collected by Ngoma was more than 20 cm long. In the same month, Ngoma went to try his luck in Nairobi, 300 km from Kiteto, to the aboriginal gemologists, where he “successfully” exchanged all 5 kg of precious stones stones for a return ticket to Kiteto, costing about $5. Thus ended the very first transaction for the sale of cutting raw materials for uncut blue tanzanite. Now you can’t even buy Amazonite at this price. When the first shacks of the Maasai miners burned down and it turned out that the brown, greenish stones (zoisites) after the fire turned into bright blue and purple crystals, which were bought in great demand by visiting traders from India and Thailand, the question of the name of the new stone arose. First we had to get rid of the word “zoisite” – the English pronunciation of the word zoisite, which is very similar to another sad English pronunciation of the word suicide (“suicide”). American jewelers and merchants had to do something. The most beautiful gemstone could have suffered the fate of an opal in Russia. But the name of Siegmund Zeuss, owner of the Austrian iron ore mine where zoisite was first discovered, was not so easy to get rid of. First “sapphire-zoisite”, then “zoisite-sapphire”, finally “Mount Meru sapphire” (Mount Meru – the name of the tanzanite mine) – everything sounded terrible. And so one of the New York jewelers with the modest surname Tiffany finally “spilled” a magnificent, diamond-framed, raspberry-blue stone under the new name tanzanite to one well-known lover of precious stones from the US Senate. And off we go. During 1968-1980, prices for cut tanzanites increased 2000 times. Not all lovers of precious stones know that zoisite is part of the epidote group and is found in nature in a wide range of colors. In addition to the usual blue and purple colors, zoisite can be pink, orange, yellow, green and brown. While the vast majority of tanzanites in the classic blue and purple hues are produced by heat treatment, other colors tend to be naturally occurring. As a gemstone, only the blue and purple color variations of tanzanite gained high popularity among buyers, while other colors remained virtually unclaimed in the market. But in recent years (abroad) there has been an increase in interest in zoisites in green, pink, and purple shades. Their prices have increased significantly. Prices for green tanzanite have increased from $100 to $1000 per carat for a three-carat stone. Prices for rare zoisite (tanzanite) in other vibrant colors have never dropped below $100 per carat. Currently, it is possible to buy faceted zoisites of rare colors (Fig. 1, 2, 3.) only for a price of no less than 300 US dollars per carat. (All prices shown are for the US market only.) Rice. 3. Lilac tanzanite from the collection www.redkiekamni.ru. Pink zoisite (Fig. 4) of gem quality is extremely rare; it is mined in Tanzania in very small quantities. Finding a stone larger than 1 carat is a great success. Along with other chromophoric elements, pink zoisites contain a predominant amount of manganese, much higher than in other color variations, which is probably responsible for its color. Rice. 4. Pink zoisite. (Hainschwang T. et al. Zoisite – More than just Tanzanite. – In Color, 2012, issue 19, pp. 44-49.) Green zoisite (Fig. 5) is also a highly coveted stone among collectors. This variety ranges in color from blue-green to yellow-green and is as rare as its pink cousin. The main deposit of green zoisites is still Tanzania, but there is information about some finds in Pakistan. The color is due to the admixture of vanadium and chromium. Rice. 5. Green zoisite. (Hainschwang T. et al. Zoisite – More than just Tanzanite. – In Color, 2012, issue 19, pp. 44-49.) The orange variety of zoisite (Fig. 6) usually has pale shades; saturated tones are practically never found. Mining takes place exclusively in Tanzania. Rare earths (cerium and neodymium) play a major role in the coloring of this exotic subgroup of stones, while the content of vanadium, chromium and manganese is insignificant. Rice. 6. Orange zoisite. (Hainschwang T. et al. Zoisite – More than just Tanzanite. – In Color, 2012, issue 19, pp. 44-49.) Yellow zoisites (Fig. 7) all have a brownish tint. Stones of bright yellow tones can only be obtained through heat treatment. However, today the mechanism of coloring of yellow zoisites is not completely clear. Rice. 7. Yellow zoisite. (Hainschwang T. at al. Zoisite – More than just Tanzanite. – In Color, 2012, issue 19, pp. 44-49.) Of course, the color of green, orange, yellow, pink tanzanites has analogues in a variety of other precious stones: tourmalines, citrines, garnets, etc. However, these are different stones. They do not possess the plechroism, dispersion, and color shades characteristic of tanzanite. That is why zoisites – “tanzanites” with a color different from the classic blue are becoming increasingly popular. The main thing that puts colored tanzanites on a par with the most expensive precious stones is their rarity.

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Tanzanite is a magnificent gemstone that, in a relatively short time since the discovery of the only deposit in the world, has found a place in the hearts of thousands of people and its niche in the gem market. This circumstance was facilitated by its unconditional beauty and rarity, as well as the fact that of all known gems, it is natural blue tanzanite that is most similar to sapphire – a favorite of all times. In this guide, we decided to address the questions of how to choose a good piece of jewelry and how much such a stone costs. To do this, consider the main parameters for assessing tanzanite. The content of the article:

Colours

First, let’s figure out what colors tanzanites come in. Tanzanite is a transparent jewelry variety of the mineral zoisite. Its color is due to impurities of various chemical elements, which is why it is so diverse, for example, iron and chromium contribute to the green color, manganese – pinkish, vanadium – blue. The classic color of tanzanite is violet-blue, with variations towards violet or blue, from light blue and lavender tones to dark blue and deep purple. Rare colors of jewelry zoisite are pink, green, yellow, and lavender. The most valuable is the rich blue, sapphire color of tanzanite, with a small content of violet (Vivid violetish blue).

Pictured: blue-violet tanzanite

For a long time, tanzanite was considered by buyers and jewelers as a rare natural imitation of natural sapphire, so a line of colors close to commercial varieties of sapphires is still in demand, for example, cornflower (cornflower blue), vivid (royal) blue – saturated blue, intense – intense blue . But all blue tanzanites contain violet to one degree or another. Separately, it is worth mentioning the most beautiful and amazing polychrome specimens; they are also called multi-colored; one such specimen contains 2-3 shades at once. For example, blue, green and purple. This distribution of shades is caused by two reasons that can be present simultaneously: crystal zoning and strong pleochroism, and their combination.

Pleochroism is the property of a crystal to show different shades in different directions. It is present to varying degrees in many minerals, but in tanzanites it is very pronounced. The main advantage is that each such specimen is essentially unique and individual, since there are no two identically colored stones. If the crystal falls into the hands of a high-level specialist, polychrome tanzanite incredibly reveals its beauty, sometimes giving birth to amazing palettes.

In the photo: a set of polychrome colored tanzanites

Such multi-colored colors are extremely rare in precious and semi-precious stones, which makes tanzanites truly non-trivial. But it happens that in some multi-colored tanzanites the overall perception of color becomes inexpressive, since the shades, overlapping each other and reflected in the facets of the stone, are mixed, as if aimlessly spreading watercolor paints of several colors on a sheet of paper.

Ennobling

In nature, transparent zoisites are mined mainly with a brownish or greenish color. Commercially attractive colors are obtained through a heat treatment process. This is a common practice for improving color, and the fact that tanzanites are heat treated does not usually affect the value of tanzanites. Keep in mind that most blue and blue-violet tanzanites are heated. At the same time, many laboratories do not have methods that can unambiguously confirm or refute warmness. Conversely, it is generally accepted that polychrome tanzanites, in which three shades are observed, are unheated. Therefore, if the natural origin of tanzanite color is fundamental to you, pay attention to multi-colored zoisite jewelry.

Weight

The weight of tanzanites, like other stones, is measured in carats (ct). The cost of a carat directly depends on the weight, that is, as the weight of tanzanite increases, the price increases. They are cut for coating and sorted by size, shade and quality. Mostly these are light bluish and bluish stones, with a purple or lavender tint. Stones up to 2-3 carats are cut into standard shapes and sizes. Tanzanites larger than 3 carats are considered individual stones and are used for making piece jewelry. As the mass increases, the stones become more saturated, large ones look dark blue and dark purple.

Cleanliness

The majority of tanzanites are gem quality and of high purity. Therefore, samples with visible inclusions are valued much cheaper than visually clean ones. The most valuable are those that are visually clean (eye clean, vvs) and with inclusions barely visible to the eye (vs – very small inclusions). For stones with inclusions, the cabochon cut is most advantageous. Also, such tanzanites are a popular material for artistic stone carving.

Cutting

Transparent tanzanites are given various shapes: oval, cushions of different silhouettes (square, rectangular, more or less round), pear. Other cuts: step (baguette, octagon), marquise, circle, trillion – are less common.

There is an unspoken fashion trend – heart-cut tanzanites, similar to the stone from the film “Titanic” directed by James Cameron. For such an idea, they often choose the shape of a wide pear, close to the heart cut, only without the characteristic depression (“slot”). Fancy cut is extremely rare. For tanzanites, the selection of pairs and sets is relevant. This is especially true for large blue and blue-violet (larger than 7 carats) specimens. This is due to the fact that tanzanites of this level are considered premium stones by default; in their price range they are valued as bright rubellites. Such pairs, as a rule, are immediately cut as a pair, achieving almost identical sizes, symmetry and proportions, therefore losses during cutting are significantly higher than when processing single stones, for which the principle of achieving maximum yield applies. It is also important to orient the crystal when cutting so that the blue color is as bright as possible. Therefore, there is a markup of 10% or more on tanzanite pairs, depending on production costs.

How to distinguish tanzanite from a fake

Tanzanite is a rare stone and is rarely counterfeited, due to its similar blue color to sapphire, tanzanite can have the same artificial imitations as sapphire.

• Glass
• Sitall
• Synthetic corundum
• Synthetic spinel

If a buyer has any doubts about whether a stone is real, we recommend contacting a reputable gemological laboratory. You will receive a certificate or expert opinion describing the main characteristics and confirming its natural origin.

Tanzanites can be similar to other natural blue stones: sapphire, indigolite tourmaline, cordierite, zircon.

In the photo: an example of an examination report for tanzanite

Evaluation

To illustrate the question “how much does 1 carat of tanzanite cost”, let’s give an example.

Let’s consider specimens of natural origin of different weights, with the most sought-after characteristics: the shade is intense violet-blue (Intense violetish blue), visually pure, with a good Asian cut. The price of tanzanite will be:

• 5 carats – from 300-320 dollars per carat
• 10 carats – from 430-450 dollars per carat
• 15 carats – from 500 dollars per carat

Keep in mind that more saturated tanzanites (Vivid and Exceptional grades) are priced more expensive, while lighter tanzanites are cheaper.

If a stone has a European quality cut, excellent polish, arch and symmetry, the stone will be valued 20-30% higher. Conversely, obvious violations in the proportions of the crown and pavilion ratio, leading to the appearance of a “window” or deterioration in play, reduce the price of a tanzanite carat. A bluer color is valued higher, a more pronounced purple color lowers the value.

Tanzanite can be considered either a precious stone or a semi-precious stone, depending on which system the gem is considered in. Precious from the point of view of the international gemological community, semi-precious from the point of view of the legal approach.

You can choose your stone in the Gem Lovers catalog.