What does cultured tanzanite mean?
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- hydrothermal method
- Horizontal directional crystallization
- history of the company
- Certificates
- Jewelry with Tyrus stones
About tanzanite
A truly modern gemstone, transparent zoisite with a natural yellowish-brown color that can be heated to a stable blue or violet color was discovered in the shadow of Mt. Kilamanjaro in 1969. Although other varieties of opaque zoisite were well known, they did not make an impact on the gemstone market. The popularity of tanzanite among jewelers and the general public was rapid and dramatic. Naturally trichroic, this species shows different colors when viewed through each of the three crystalline axes: blue, red-violet, and yellow-green.
Although blue-violet stone is sometimes found in a rough state (Mother Nature has already provided the heating in this case); the vast majority of them need to be heated to get that color. Typically the stones are cut and polished before heating to about 700 degrees Fahrenheit, since abrasions, cracks and inclusions in the raw material can cause cracking. This means that the cutter must try to orient the stone to get the best color before the color changes. It is a yellow-green color that is changed to colorless by this treatment, leaving only the other two more attractive color axes.
Another important decision a cutter must make is whether to select size (usually a more purple orientation produces the largest stone) or blueness (blue orientation produces smaller stones). A very small portion of raw tanzanite is heat treated to a green or blue-green color, and such stones are prized by collectors. (Technically they should be called heated green zoisite, but everyone calls them “green tanzanite” anyway.)
In the trade it is assumed that all tanzanites are heat treated and the color remains stable. Blue stones were initially prized as a substitute for sapphire, but more purple tones gradually grew in popularity. Tanzanite is often used as a ring stone, but due to its 6,5 hardness, daily wear dulls the finish and its brittleness poses a risk. It is best suited for earrings, pendants, tie pins, and with carrying rings or protectors. Recent catastrophic weather conditions, mining accidents, government embargoes and ongoing political tensions have limited supplies, especially of larger, finer-colored stones.
Value
In general, stones with more blue color are valued higher than stones with a more purple hue, and a medium dark color is ideal. Custom cuts add value. As always, size and clarity have a strong impact on prices -> clean large rough diamonds are extremely scarce and exports are now limited, so larger gemstones are rapidly rising in price and becoming increasingly scarce in availability. Collectibles such as greens or ultra-rare cat’s eye stones are highly sought after and quite valuable.
Features
Compound:; calcium, aluminum, hydroxysilicate Ca2Al3 (SiO4) 3OH Gloss:; glassy Hardness:; 6,5 Crystal structure:; orthorhombic Fracture:; concoidal to irregular Cleavage:; 1, ideal Density:; 3,35 Refractive index:; 1,69 Birefringence:; 0,010 Pleochroism:; trichroic, blue, red-violet, yellow-green
When we hear the phrase “synthetic stones,” many associations come to mind. Unfortunately, they are often not based on a scientific definition. Therefore, the purpose of this article is to systematize knowledge and understand what is what in the world of precious stones.
Firstly, all stones can be divided into 2 large groups: natural and artificial.
Among natural stones, everything is not clear. It is possible to distinguish non-ennobled and ennobled (in the English version “treated”) groups. There are many ways in the world to refine (improve) stone: from heating it on household tiles to covering it with a layer of special high-tech glass.
Of course, all-natural specimens are valued most highly. However, the largest volume on the market, for example, of sapphires is occupied by heated ones. And this is absolutely normal, since the color is naturally quite faded or too dark. Refining makes the stone a brighter and more noticeable color.
Various impregnations are used for certain types of stones (opals, turquoise or emeralds). And some types of raw materials can be irradiated (topazes, quartz).
As for “synthetic stones”, there are also several concepts here. Typically, artificial stones are divided into two large groups:
- grown / recrystallized / synthetic stones (eng. “created”, “lab created”, “lab grown”, “man-grown”, “grown”, “recrystallized”, “synthetic gem”);
- imitation.
The first group includes stones that are 100 percent identical to their natural counterpart, and imitation includes any materials that in their appearance may be similar to a precious jewelry insert.
Grown stones have exactly the same composition, all physical and optical characteristics and grow under almost the same conditions as their natural brothers. In Russia, in a laboratory gemological certificate for such stones they write, for example, “synthetic emerald.”
There are several methods for obtaining grown stones, but they all boil down to one idea: grind low-quality natural raw materials of the corresponding mineral, stabilize the required color using the same natural elements, melt the resulting charge (powder) and make the crystal grow again. Recrystallize under supervision. In fact, in the laboratory, absolutely the same crystal formation process is created as in nature, but a person significantly speeds it up, controls the color and provides the necessary parameters of the gemstone. However, the growth cycle can take several months.
Often the technology involves the use of precious metals with their special physical and chemical properties. Of course, this also affects production costs.
Without false modesty, RusGems is the largest manufacturer and aggregator of grown stones in the world. For more than 20 years of work, we have produced and collected all possible types of raw materials and stones. Including unique samples that are not even in major gemological museums in the world (for example, Stepanov’s ruby or yttrium orthoaluminate). Today we have more than 200 types of raw materials, which we sell and cut to order.
Nowadays, the most popular grown stones for creating colored gemstones are:
- Verneuil method*** (for fabulite and rutile);
- Czochralski method*** (for sapphires, spinel, alexandrite, tanzanion, rare earth garnets (GGG and YAG);
- hydrothermal method*** (for emeralds and beryls of other colors, sapphires and quartz);
- zone melting method*** (for rubies and chrysoberyls, including alexandrite).
The following can be used as imitation gemstones:
- glass,
- different types of ceramics,
- cubic zirconia,
- plastic,
- Nanosital.
For example, you can take yellow cubic zirconia: it is completely identical in color to both citrine and yellow sapphire. Thus, it can be used as an imitation of both of these precious inserts. At the same time, cubic zirconia in its composition and properties is not related to any mineral.
It is incorrect to call imitations synthetic rubies, emeralds or, for example, diamonds, because:
- firstly, in the certificates of such stones it will be written: “glass, glass ceramics, cubic zirconia” and so on, that is, exactly the type of material without indicating any precious mineral;
- secondly, they have a unique composition that is not related to any gemstone;
- thirdly, imitation is usually a monoproduct with the same physical and optical characteristics, but of different colors (cubic zirconia can imitate sapphire, topaz, aquamarine, diamond, quartz, etc.), while each natural gemstone has its own unique set of optical and physical properties.
Naturally, an important issue remains the ability to distinguish synthetic stone from natural***. Unfortunately, there is no universal answer; it requires experience, knowledge of the specifics of specific types of stones, their color characteristics, shine, types of inclusions, etc.
Therefore, within the framework of a conversation about the artificial origin of a stone, consistency and some gemological experience are necessary. It is best to buy certified stones from trusted suppliers.
The concept of “synthetic stone” is very broad and not always clear. It is quite obvious that in the modern world synthetic stones have occupied their large niche. And it’s not just about the relatively low price and convenience for large factories. Now the decisive factor is beauty, attractiveness and originality. All this is provided by synthetic stones. Cheap or expensive, rare or ubiquitous – they will help solve any given problem. And crystal growth in the laboratory is one of the most funded areas of development in the jewelry industry.
