Green diamonds are very unusual because their colour comes from exposure to natural radiation. As the pure diamond crystals were forced from deep within the Earth's crust toward the surface, natural radiation made the colour change.

All coloured diamonds are rare, usually rarer than classic clear white diamonds. For every 10,000 clear diamonds mined, there is just one coloured diamond. Most coloured diamonds receive their colour from trace impurities that become part of the otherwise pure carbon that forms diamond crystals. Radiation makes green diamonds almost unique in nature.

Because radiation can be used to create green diamonds in laboratories, it can be difficult to tell the difference between a natural and treated green diamond. In this article, we will describe how to tell the difference between natural green diamonds and those that have been enhanced or manufactured in a laboratory. You will also discover how to get the best value for your money when you buy one of these beautiful gemstones.

What Is A Green Diamond?

A green diamond is just like the more common colourless or white diamonds we are used to seeing in jewellery. Pure green diamonds are quite rare; usually, there is another hue caused by impurities.

Because the green colour of the diamond is produced by radiation altering the structure of the crystal, the colour effect is often found only on the outer surfaces of a diamond crystal. The inner part of the rough diamond can be clear. When the diamond is being cut to make jewellery, the cutter needs to take great care not to expose the clear crystal below the green coloured layer.

Many coloured diamonds, including green ones, are assessed and graded according to the 4Cs of cut, colour, clarity and carat weight devised by the Gemological Institute of America (GIA). Clear diamonds place an emphasis upon clarity, Coloured diamonds gradings emphasise the colour, often at the cost of clarity. Many of the green diamonds used in high-quality jewellery have more significant flaws than would be acceptable in a clear diamond.

Not All Green Diamonds Are Natural

The rarity of green diamonds has led to the creation of treated diamonds. These laboratory enhanced gems are treated with radiation in just the same way as if they were underground. It is tough for even experienced diamond experts and grading labs to tell a colour enhanced diamond from a naturally coloured one.

To help graders and buyers tell natural diamonds from treated or synthetic stones, it is common for diamond cutters to leave a small unpolished area on the girdle of the stone. The unpolished area reveals the brown staining that is typically found on uncut green diamonds.

Synthetic Or Treated Green Diamonds

In addition to natural diamonds treated to create their green colour, there exist green diamonds that are entirely lab-created. These diamonds are physically and chemically identical to natural green diamonds. Synthetic diamonds are very hard to tell from the real thing. Because green diamonds are both rare and not very popular for use in jewellery, even in their synthetic form, they are rare. Synthetics vary from natural diamonds in one fundamental respect: they do not have the surface browning caused by radiation that is a characteristic of natural green diamonds. This makes the unpolished area on the girdle on many natural stones the easiest and most certain way to tell real from fake.

Jewellers should always tell buyers when the diamonds they are about to buy are enhanced or treated. Unfortunately, this does not always happen. Buyers can end up overpaying for colour treated diamonds when they had expected to become the owner of a natural green diamond.

If you know what you are buying, a colour treated diamond can be an economical way to own a beautiful piece of green diamond jewellery. The safest way to ensure that you get what you paid for is to make sure that your diamond comes with a grading report from a reputable lab such as the GIA.

Figure 1. Image of colours and intensities of green diamonds. image and caption text courtesy: https://www.leibish.com/about-natural-green-diamonds-article-507

The image above depicts images of green diamonds with different overtone colours in the various intensity grades. The green colour scale is shown line by line from left to right:

First line: Fancy Light, Greyish Green Chameleon, Fancy Greyish Green Chameleon, Fancy Deep Grey, Yellowish Green Chameleon, Fancy Dark Grey Yellowish Green Chameleon, Fancy Light Greyish Yellowish Green, Fancy Greyish Yellowish Green

Second line: Fancy Grey Yellowish Green, Fancy Dark Grey Yellowish Green, Fancy Yellowish Green, Fancy Intense Yellowish Green, Fancy Vivid Yellowish Green, Fancy Deep Yellowish Green, Fancy Light Yellowish Green, Fancy Yellow Green

Third line: Fancy Intense Yellow Green, Fancy Vivid Yellow Green, Fancy Deep Yellow Green, Faint Green, Very Light Green, Light Green, Fancy Light Green, Fancy Green

Fourth line: Fancy Intense Green, Fancy Vivid Green, Fancy Deep Green, Fancy Grey Green, Fancy Greyish Green, Fancy Deep Greyish Green, Fancy Light Bluish Green, Fancy Bluish Green

Fifth line: Fancy Intense Bluish Green, Fancy Vivid Bluish Green, Fancy Deep Bluish Green, Fancy Light Blue Green, Fancy Blue Green, Fancy Intense Blue Green, Fancy Vivid Blue Green, Fancy Deep Blue Green

How Green Coloured Diamonds Are Graded

The GIA colour grade for coloured diamonds is quite different from the one for clear gemstones. The colouration of the diamond is assessed according to its primary and secondary hue (colour) and intensity.

Green Diamond Secondary Colours

The colours generally associated with green diamonds are grey, blue and yellow. Where the green colour is dominant, a GIA grading report will show the colour in two words as, for example, greyish green. This tells the buyer that the primary colour is green, and the secondary colour is grey. If the grey colour is dominant, then the colour would be reported as greenish-grey.

The yellow colouration is from trace amounts of nitrogen in the diamond structure. Blue and grey come from trace amounts of boron.

Green Diamond Colour Intensity

The intensity, the depth of the colour in the diamond is reported using the following scale:

Faint Green, Very Light Green, Light Green, Fancy Light Green, Fancy Green, Fancy Intense, Fancy Vivid, and Fancy Deep.

The rarest and most valuable green diamonds are those with the deepest colours Fancy Vivid and Fancy Deep, combined with pure green colouration without a secondary colour: Fancy Vivid Green and Fancy Deep Green.

GIA Colour Grading Reports

For coloured diamonds, the GIA provides two types of report. The first is a report into the colour alone. There is no reference to clarity, cut or carat weight. The second type gives the same information about clarity, cut and carat as their standard reports.

In both reports, the GIA records the source of the green colour of the stone, whether it is naturally coloured or treated. This is the most reliable way to know what type of diamond you are buying.

When you own jewellery made with green diamonds, you own something that is both beautiful and unusual. If you make sure that you are buying the diamond you want, whether it is synthetic, treated or natural, you have something that you can be proud of for a lifetime!