Diamonds Go Green for St. Patrick's Day
Green diamonds are amongst the rarest diamonds in the world. The GIA reports that just 0.4% of all diamonds sent to the lab in the last ten years were green. Green diamonds tend to be small, with the largest green diamond ever sold at auction weighing just 5.03 carats. It is a fancy vivid green diamond called the Aurora Green Diamond and sold at auction in 2016 for a record-breaking $16.8 million.
What causes colour in diamonds?
In general coloured diamonds are a result of structural irregularities or the presence of trace elements in the crystal structure. A diamond that forms into a structurally perfect crystal and is chemically pure, will result in a clear white diamond. However more often than not there are hiccups along the way leading to plastic deformation or inclusion of trace elements in the crystal structure.
Red and pink diamonds are thought to be created by plastic deformation of the crystal structure - the pressure under which these crystals were formed has caused the structure to "slide" sideways distorting the path of light through the gem and showing up red or pink.
Yellow and blue diamonds are caused by trace element of Nitrogen or Boron included in the crystal structure. Whereas salt&pepper or black diamonds are coloured by carbon inclusions.
So what colours a green diamond?
A green diamond starts out as any other diamond, but it is exposed to atomic irradiation from radioactive substances - such as naturally occurring radioactive uranium. The irradiation results in a displacement of atoms in the crystal structure, which interferes with the light absorption and refraction, causing the diamond to reflect a green hue. The longer a diamond is exposed to irradiation the deeper the colour will be.
Note that the diamonds do not absorb the irradiation - ie green diamonds themselves are not radioactive - but the exposure results in a green hue. Most green diamond rough is coloured only at the surface and the cut gem shows only the faintest colour. Green diamonds with a green body colour (i.e. green throughout) are exceedingly rare.
Sometimes the colour is not uniform, but may show some yellowish or brownish areas known as "irradiation stains". Interestingly it is not possible to recreate these stains in a laboratory setting (more about that later), so they are an immediate tell as to the natural origin of the gem.
What to look for when buying green diamonds
Hue, Tone & Saturation
For fancy coloured diamonds, the GIA has a unique color-grading system that takes into account the hue (colour), tone (light-dark), and saturation (intensity). Higher grades are assigned to the richer, deeper hues, as they are rarer.
Green diamonds are graded for tone and saturation, but often have a secondary colour. For example a green diamond may be classified as "Fancy Intense Green diamond with a Bluish secondary tint".
Enhanced Green Diamonds
So far we have discussed naturally occurring green diamonds - where the diamond crystals are exposed to hundreds of thousands of years of naturally occurring irradiation.
But nowadays the effect of irradiation can be recreated in a laboratory setting. Natural diamond may be bombarded with with irradiation leading to similar colours. As it is a tricky and expensive process it is not a common procedure, but these "enhanced" green diamonds are available at more accessible prices. They make an excellent substitute for the more costly natural green diamonds.
Lab-Grown Green diamonds
Another source of green diamonds are lab-grown diamonds. These are diamonds that are grown in a lab environment that closely resembles the environment necessary to produce a natural green diamond. The resulting diamonds are exact replicas of their natural counterparts. They are structurally and chemically the same as a natural green diamonds and the only way to tell the difference is by using specialised laboratory equipment. (oh and of course the tell-tale yellow or brownish stains that may occur on natural green diamonds as they cannot be recreated in a lab setting.)
Because the conditions used to create natural and lab-created green diamonds are so similar, the majority of green diamonds are tested for their "origin of color" by the GIA before being put on the market.
It becomes immediately obvious why it is important to get a diamond report from a reputable laboratory when you purchase a green diamond. Especially for coloured diamonds we recommend getting you diamond report from the GIA - The GIA is recognised worldwide as the leading laboratory for grading diamonds. The diamond report will confirm whether your gem is natural, enhanced, or lab created.
Green Diamonds at DesignYard
As green diamonds are exceedingly rare, it follows that we do not have a big selection in the gallery. However we'd be delighted to show you a few select pieces. Book your appointment here.