While many of the basics of how to buy a diamond apply to all diamond types, they vary a bit among the different colours. Such is the case with natural green diamonds which are the most alluring and intriguing in the family of fancy colour stones. Let’s take a look and find out which factors to consider to make a good investment.
What Are Green Diamonds?
Natural green colour diamonds are among the rarest of the fancy colour diamond family. They owe their beautiful colour to a small content of radioactive chemical elements such as uranium or thorium.
The natural green colour developed when the radioactive materials decayed and penetrated nearby diamond crystals forming deep in the earth’s crust over millions of years. In simple words, the result of the colour is knocking electrons or carbon atoms out of their position, usually in the outer layer of the diamond’s crystal structure. That is the reason the green colour is often present as a shallow layer on the outside of the diamond crystal and diamonds with a uniform green colour are exceptionally rare.
The displacement of carbon atoms and electrons in the diamond’s crystal structure changes the way light travels through the stone. Such deformation causes the diamond to selectively absorb the light entering the stone and transmit wavelengths in the green portion of the spectrum, giving the diamond a green colour.
Although radiation is the most common cause of green colour in diamonds, it can also be caused by structural defects in the diamond’s crystal structure because of the presence of nitrogen, nickel and hydrogen atoms.
How to Choose the Colour of Green Diamonds
A green diamond’s colour grade is based on both the colour of the stone and its intensity level. According to the GIA green diamonds are classified using the following colour grades: Faint Green, Very Light Green, Light Green, Fancy Light Green, Fancy Green, Fancy Intense Green, Fancy Vivid Green, and Fancy Deep Green. The secondary colour is also included in the grade if it is present. The most common secondary hues include yellow, brown, blue and grey colours.
The colour evaluation of green diamonds has three main components: hue, saturation and tone.
Hue is the visible colour of a diamond, and the primary hue of green diamonds is green.
There can also be secondary hues which greatly affect the value of stones. The most common secondary hues present in green diamonds range from yellow, yellowish, blue, bluish, brown, brownish, grey, greyish, grey-yellowish, and greyish-yellowish.
Secondary hues that enhance the primary hue or do not detract from it add the value as a rule. For example, green diamonds with blue secondary hue command higher prices than the diamonds with grey, yellow or brown hues.
Natural green diamonds with no secondary hues are the rarest and the most expensive as a result.
This characteristic refers to the intensity of the colour.
As a general rule, the more saturated the colour of a diamond, the more valuable it is. That is why the diamonds that have pale or faint green colour are less desirable than those with deep and vivid green colour.
This characteristic refers to how light or dark the colour is.
The choice of the tone depends on your personal preference, however, the stones that are somewhere in the middle are the most sought-after.
The colour grade of green diamonds is assigned based on saturation and tone.
How To Choose The Clarity Of Green Diamonds
The clarity of green diamonds is graded the same way as that of colourless stones. The fewer inclusions, the higher the clarity grade.
Of course, high clarity green diamonds are more valuable, but this characteristic is not crucial for fancy colour diamonds. The green colour tends to hide imperfections, so the appearance of green diamonds is less affected by flaws compared to white diamonds.
When choosing the clarity of green diamonds, look for a stone that is eye clean, meaning the diamond should not have inclusions visible to the naked eye.
Green diamonds in the SI1-SI2 clarity range may look stunning and do not differ significantly from diamonds in VS or even VVS range.
How To Choose The Cut Of Green Diamonds
Unlike colourless diamonds, green diamonds are not cut to maximize brilliance and sparkle.
Green diamonds are cut to achieve the best colour possible as most natural greens have a colour that is only “skin deep”. That means cutters often try to preserve green colour around the girdle of the stone or to preserve colour in the culet. In other words, the proportions that are considered ideal for colourless diamonds will not always be the best to bring out the colour of green diamonds.
So when choosing a green diamond, you should focus more on the stone’s colour intensity and hues, rather than judge the diamond using traditional cut grades.
Green Diamond Rarity and Prices
Since good quality green diamonds are more difficult to source, they are much more expensive and valued than other coloured diamonds, even though green diamonds are technically less rare than reds, for example.
Pure green diamonds are the most desired and expensive gems; however, they are also the rarest among the greens. The presence of a secondary hue has a great impact on the diamond’s price. For example, the blue hue always increases a green diamond’s price, while the yellow or grey hue usually makes a green diamond more affordable.
Cover image credit: Sotheby’s