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How to choose a tanzanite

June 25, 2021

natural tanzanite cushion from Gem Lovers collection

On the photo: natural tanzanite cushion from Gem Lovers collection

Tanzanite is a magnificent gemstone which has found a place in the hearts of thousands people in the relatively short time since the discovery of the only one deposit in the world. It was promoted by its beauty and rarity. And it looks very similar to very popular and more expensive gemstone – blue sapphire. In this guide we decided to answer on questions about how to choose a good stone and how much such stone costs. Consider the main parameters for evaluating tanzanite:

Colors

Let’s see what colors tanzanites are. Tanzanite is a transparent gem variety of the zoisite mineral. Its color is due to impurities of various chemical elements. For example iron and chromium contribute to green color, manganese – pinkish, vanadium – blue. The classic color of tanzanite is violet-blue, with variations in the direction of violet or blue, from light blue and lavender shades to dark blue and dark violet. Rare colors of gem zoisite are pink, green, yellow, lavender. The most valuable is considered vivid blue, sapphire color of tanzanite, with a small content of violet (vivid violetish blue).

For a long time tanzanite was considered by buyers and jewelers as a rare natural analog of natural sapphire, so the range of colors close to commercial sapphire varieties is still in demand. For example, Cornflower Blue and Vivid Blue (Royal Blue). But in all blue tanzanites, violet tint is also present. Also it is worth mentioning the most beautiful amazing polychrome specimens. They are also sometimes called multicolour tanzanites. In one such sample 2-3 shades are immediately presented. For example blue, green and purple. This distribution of shades is caused by two reasons that may be present simultaneously: zoning of the crystal, very strong pleochroism and also their combination.

Pleochroism is the property of a crystal to show different shades in different directions. It is present to one degree or another in many minerals, but in tanzanites it manifests itself very strongly. The main advantage is that each such specimen is essentially unique and individual, since there are no two equally same colored stones. If a crystal will go to the hands of a high-level cutter polychrome tanzanite unbelievably reveals its beauty, sometimes giving birth to amazing colors.

Such multicolour stones are extremely rare. It makes tanzanites truly nontrivial. But it happens that in some multicolor tanzanites the general perception of color becomes inexpressive since the shades overlapping each other and being reflected in the facets of the stone mix.

Treatment

Transparent zoisites are mined mainly in a brownish or greenish color. Commercially attractive colors are obtained by heat treatment. This is a common practice for improving color. And the fact of heat treatment does not usually affect the cost of tanzanites. Keep in mind that most blue and blue-violet tanzanites are heated. At the same time many laboratories don’t have methods that can confirm or refute heating. It is generally accepted that polychrome tanzanites are unheated if all three pleochroic colors are observed. If you need natural origin of the tanzanite color pay attention to multicolor gem zoisites.

Weight

The weight of tanzanites is measured in carats (ct). The price of a carat directly depends on the weight. With an increase of the weight price also increases. They are faceted for calibration small sizes. It sorted by size, shade and quality. Usually they are light bluish and medium bluish stones with a purple or lavender hue. Stones up to 2-3 carats are limited by standard shapes and sizes. Tanzanites larger than 3 carats are considered individual stones and are used for creating single jewelry pieces. The stones become more saturated as the weight increases. Large ones look dark blue and dark violet.

Clarity

The most part of tanzanites are gem quality with high clarity. That is why samples with visible inclusions are priced much cheaper than eye clean. The most valuable types are Eye Clean, VVS (Very Very Small Inclusions) and VS (Very Small Inclusions). The cabochon cut is most advantageous for stones with inclusions. Also such tanzanites are a popular material for carving.

Cut

There is an unspoken fashion trend – tanzanites with a heart shape similar to the stone from the “Titanic” movie directed by James Cameron. Under such an idea, the shape of a wide pear is often chosen, close to the heart shape, only without a characteristic “slot”. Fancy artistic shapes are extremely rare. For tanzanites the selection of pairs and headsets 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 terms of price range they are valued as bright rubellites. Such pairs are immediately cut as a pair as a rule reaching almost the same size, symmetry and proportions. Therefore losses during cutting are significantly higher than when processing single stones for which the principle of achieving maximum yield is valid. When sawing, it is also important to orient the crystal so that, if possible, the blue color should be oriented for the table. That is why pairs of tanzanites is an extra charge of 10% and higher, depending on the costs of production.

How to distinguish tanzanite from a fake

Tanzanite is a rare stone and it is rarely faked because of its similarity to blue sapphire. Tanzanite can have the same imitations as sapphire. There are materials like these:

  • glass
  • sitall
  • synthetic corundum
  • synthetic spinel

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

Tanzanites can be similar to other blue stones: sapphire, indicolite tourmaline, cordierite and zircon.

Price

We give an examples here to illustrate the question “how much does 1 carat of tanzanite”.

Let us consider specimens of natural origin of different weights,with the most popular characteristics: a shade of saturated violet-blue (Intense violetish blue), eye clean, of good asian cut. The price of tanzanite is:

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

Keep in mind that best color tanzanites (grades Vivid and Exceptional) are priced more expensive, and lighter – cheaper.

If the stone has a cut of european quality level, excellent polishing, proportions and symmetry the stone is rated higher by 20-30%. And obvious violations in the proportions of the ratio of the crown and the pavilion, leading to the appearance of a “window” or a deterioration of luster reduce the price of a carat of tanzanites. More blue is valued higher, more violet reduces the price.

You can choose tanzanites in the Gem Lovers catalog.

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