Green diamonds are one of the most difficult diamonds to value and understand on the coloured diamond market.
The reason for this is the way in which green diamonds are formed. Caused by exposure to natural irradiation during the diamonds formation, the colour of green diamonds can either be throughout the stone or just present on the surface. What expert cutters are now doing is leaving “skin” or surface radiation staining on the stone to give the appearance that the stone is greener than it is.
Because the GIA grades colour on face up appearance and because the skin is natural there is little indication how the stone appears green. Generally how one can tell is to view the diamond loose and see how much of the stone is in its rough form, the less the better.
Green diamonds with the same GIA grades can be fractions of one another in value because of green “skin”. This should not deter a collector from purchasing a skin stone however because a natural green diamond is extremely rare in any form.
Colours of green diamonds include brown, yellow, grey and blue. Brown and Grey are similar in that they greatly reduce the value of a stone. Stones of this nature have more tone than their saturation allows and create what most people believe are less attractive colours.
Yellow as a modifier also devalues a diamond but in some cases can create vibrant colours. These stones are extremely saturated and can be described as neon in colour. What should be searched for are stones ending with green, such as fancy intense yellow green, when one is looking for these “neon” coloured stones.
Finally blue as a modifier is the most valuable of the two hued stones. Creating colours comparable to tropical waters these diamonds are extremely rare and beautiful.
Another type of diamond exists called Chameleon diamonds. These stones display a change in colour after having been stored in darkness or when gently heated.
Their resting colour is usually a combination of green yellow and grey and change to a orangey yellow. What is usually searched for when collecting Chameleon diamonds is a stone that has a green base colour (example: Greyish Yellowish Green).