Geological classification

What is the difference between a grown diamond and a natural one?

An artificial diamond is a stone almost identical in composition to a natural diamond, grown under special laboratory conditions. Do not confuse artificial diamonds with cubic zirconia and moissanite. If with the last two a natural diamond has many differences that make it possible to identify a fake using even home tests, then in the case of an artificial diamond everything is much more complicated. Let’s try to figure it out.

Artificial diamonds – what are they and how are they made?

The first artificial diamonds were synthesized back in the 50s of the 90th century. But it was only in the XNUMXs that samples were brought to sizes that would be of interest to the jewelry industry. Today there are two main production technologies.

Synthesis of HPHT

The technology of growing diamonds in small capsules under high pressure (from high-pressure high-temperature – “high pressure and temperature”). The raw material is diamond powder, which is dissolved in molten metal flux and then crystallized on a seed. The growing process takes from a couple of weeks to several months. Most HPHT diamonds are yellow, orange-yellow, or brown-yellow in color. By adding inhibitors, transparent and blue stones are obtained, and by adding boron, blue stones are obtained.

CVD synthesis

The technology of growing diamonds using a laser inside a vacuum chamber filled with carbon-containing gas (from chemical vapor deposition). The laser destroys gas molecules, causing carbon atoms to settle on the seed plates. The growth rate is several weeks. CVD technology allows you to grow several samples simultaneously. Most CVD diamonds are brown or gray in color. When nitrogen or boron is added to the chamber, yellow, pink-orange or blue stones are obtained. To obtain clear samples, CVD brown diamonds are decolorized using HPHT technology.

How to distinguish a natural diamond from a synthetic one

Unfortunately, for ordinary people, determining the naturalness of a stone is only possible with the help of special gemological equipment and tests.

Color zoning

  • Colored diamonds grown using HPHT technology have color zoning according to a geometrically ideal pattern.
  • Natural diamonds may also exhibit color zoning, but it will not follow any geometric pattern.
  • CVD diamonds have a perfectly even color distribution throughout the entire sample.

Thus, using a microscope, a gemologist can understand which stone is in front of him based on the type of color zoning.

Metal and graphite inclusions

Due to the peculiarities of the technology, HPHT diamonds often have inclusions of hardened metal, while CVD diamonds often contain graphite. They can only be seen with very high magnification. But HPHT stones react to a strong magnet: up to 95% of samples of such synthetic diamonds have magnetic properties. Thus, the magnet test allows only HPHT diamonds to be “rejected”. A detailed examination of samples under powerful magnifying technology will reveal inclusions of metal and graphite, which will most likely indicate the synthetic nature of the stone.

Note that natural diamonds can also contain inclusions of graphite, ilmenite, magnetite, garnet, malacolite, etc. But, as a rule, these inclusions have a typical “feather” appearance – an experienced gemologist can immediately determine their natural origin.

Interference (deformation) of colors

This test is based on placing the diamond between two polarizing filters at an angle of 90 degrees to each other. Natural stone will exhibit a cross-hatching or mosaic pattern of color interference that occurs due to uneven pressure being applied to the crystal during the growth period. Synthetic stones grown at constant pressure values ​​do not show a color deformation pattern.

Fluorescence

The fluorescence of synthetic diamonds has a characteristic pattern. For HPHT stones it has a cross-shaped shape, and for CVD stones it has a striped pattern. Under a UV lamp, HPHT synthetics often have a green, yellow-green or yellow color, while CVD synthetics are predominantly orange or red. But natural diamonds glow blue.

Figure 1. On the left is a CVD diamond, in the center is an HPHT diamond, on the right is a natural diamond.

A special DiamondView installation allows fluorescence visualization to reveal patterns of crystal growth. Based on the picture, it becomes clear which sample is in front of the gemologist – HPHT, CVD or natural stone. Unfortunately, the cost of installation is so high that they are not found in domestic laboratories.

Figure 2. Cross-shaped patterns of HPHT diamonds when viewed on DiamondView.

Phosphorescence

After turning off the UV lamp, natural stones “go out”, but synthetics (especially HPHT) can glow for more than a minute.

To summarize, we can say that to accurately determine the origin of a diamond, special expensive equipment is needed: refractometers, ultraviolet gemological lamps, polariscopes and microscopes. They cannot be found in all laboratories. Therefore, in order not to guess what kind of stone you purchased, it is better to make purchases exclusively in trusted places.

All diamonds in our showroom are completely natural. They are certified by the independent gemological center of Moscow State University. The stones are accompanied by a certificate indicating the main characteristics of natural stone, as well as a number and a link to the test laboratory report.

Independent expert gemologist. Academic titles: GG GIA (Chartered Gemologist, Gemological Institute of America), AJP GIA (Accredited Jewelry Professional of the Gemological Institute of America), MBA Kingston University UK (Master of Business Administration from Kingston University UK).

Author of the best-selling book “Precious Stones”.

Other expert publications:

  • Evaluation of colored jewelry stones. Introduction to the “World of Color” from GemGuide
  • Field test of Diamond Inspectors
  • Synthetic Diamonds 2020
  • How to evaluate a gem or a game without rules
  • Let’s talk about the new GOST for diamonds

Progress is still a strange thing. You never know at what angle he can turn a well-known problem so that it becomes the most painful. Synthetic diamonds have been known for a long time. In 2016 and 2017, on the pages of this magazine, we already discussed how the massive appearance of synthetics could potentially affect the jewelry market. 2018 made its own adjustments. Now no one has a problem with large synthetic diamonds, whether set in a piece or not. Nowadays, only a very arrogant scammer will try to sell a client jewelry with a one- or two-carat artificial diamond. There are no problems recognizing large stones.

The main misfortune of today is synthetic melee diamonds. Small stones for “sprinkling”, with a diameter of 0,6 to 3,5 mm, are sold and bought in the thousands of carats. If synthetics are mixed into such a batch with natural diamonds, then identifying such a mix is ​​incredibly difficult. No magnifying glass or simple thermal and electrical conductivity detectors will help identify fraud. Synthetic diamonds are no different in appearance or physical characteristics from natural stones. To continue the conversation, let’s remember what synthetic diamonds are and what types they come in.

All colorless, shiny stones that may or may not be diamonds and set in your jewelry can be roughly divided into five types:

1. Real natural diamonds, without signs of refining, that is, without obvious human intervention in the natural structure of the stone.

2. Natural diamonds whose color is enhanced using HPHT (High Pressure High Temperature) technology. Not all diamonds are susceptible to this effect. This method is mainly used to improve the color of relatively large natural stones, weighing from 0,5 carats. Visually, such diamonds are no different from untreated ones. The fact of color improvement can only be revealed by laboratory testing.

3. HPHT (High Pressure High Temperature) Synthetic Diamonds. They are completely created by man in special installations. In terms of chemical composition and physical properties, these stones are almost no different from natural diamonds. Until recently, HPHT synthetics had only a few distinctive features. These were mainly unusual luminescence and magnetic metallic inclusions. In ultraviolet light, a special pattern could be seen in such stones – a “cross”, and the luminescence color was usually from yellowish-green to green. However, the improvement of technology has led to the fact that these characteristics do not always appear in modern synthetic diamonds. There may be situations when you get HPHT synthetics without luminescence and without magnetic metallic inclusions.

4. Synthetic diamonds CVD (chemical vapor deposition technology). This is a more modern method of diamond synthesis compared to HPHT. Not many key features of CVD stones are known. This is mainly an unusual fluorescence color (orange), but there are cases where CVD-grown diamonds do not fluoresce at all or show a very real blue tint of natural diamond in short and long ultraviolet light.

5. Synthetic CVD diamonds whose color is enhanced by HPHT. Mainly applied to PT color stones in the GIA 4C color nomenclature for colorless diamonds. With this type of treatment, stones with a noticeable yellow or yellow-brown tint are improved to I GIA color. The hue of fluorescence may change from orange to natural bluish or not quite natural bluish-green. A phosphorescence effect may occur when, after exposure to UV rays, the diamond continues to glow on its own in the dark from several seconds to several tens of minutes.

We will not discuss the option with imitation diamonds in this article, since distinguishing a natural or synthetic diamond from glass, cubic zirconia, moissanite or titanite does not present any problem.

Unfortunately, despite a detailed description of the characteristics of synthetics, none of the listed characteristics allows one to reliably distinguish artificially grown diamonds from natural ones. Only spectral analysis can give an accurate answer. However, such equipment is not available everywhere.

And yet, a reliable key sign of synthetics exists, although it cannot be seen with the naked eye. We are talking about the content and distribution of the chemical elements nitrogen and boron in the diamond crystal lattice. Depending on the presence or absence of nitrogen atoms, as well as the nature of their distribution in the crystal lattice of the mineral, diamond is classified into one of five types. All of them are shown in Table 1.

Table 1. Classification of diamond types according to the content and distribution of nitrogen and boron atoms in the crystal lattice.

Diamond type based on nitrogen and boron content

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