Green diamonds are created by a set of unique geological factors involving natural radiation. Uranium and Thorium, as well as their decay products, are the main radioactive elements involved both in earth mantle rocks and corrosive hydrothermal fluids as well as ancient mostly secondary heavy mineral deposits. Exposure to the various forms of radiation emitted by these elements over millions of years can cause localized damage throughout the crystal lattice of a diamond creating what is known scientifically as a General Radiation Centre. These GR centres in combination with both Nitrogen N3 clusters and brown graining absorb red to orange light wavelengths inside a diamond and together recombine returning light rays to the observer as green. Unfortunately the majority of green rough, usually Type Ia & IIa, only holds skin-deep colouration due to alpha ray damage and loses its tinge immediately upon cutting.
To ascertain the natural origin of the green colour the GIA always strictly requires remnants of the original rough ‘skin’, so-called ‘naturals’, to be preserved on any polished diamonds. Such naturals must feature (naturally annealed) brown or dark green radiation spots or patches as evidence.
Although green diamonds are not rare, virtually all are slightly color-modified being either brownish, greyish, yellowish or bluish green. Highly saturated vivid or deep green diamonds, reminiscent of foliage or bottle glass respectively are however exceedingly rare. The market prefers pure greens, followed by those containing blue secondary hues combining to bluish Green akin to mint-greens. A striking exception is turquoise Blue-Green stones from Brazil which are valued similarly to or may even surpass ‘straight’ green stones. Yellowish Greens and Yellow-Greens are a distant third and considered fairly common. These aforementioned hues are all generally bright in appearance, much in contrast to greyish Greens belonging mostly to Type Ia and brownish Greens which are rather dull and never reach intense or vivid saturation. These latter two hues conclude the value scale.
Green transmitters, unusually intense and vivid neon yellowish to lime green diamonds in which daylight triggers additional yellow to green fluorescence play a rather unique role. Hydrogen (H3) aggregates of 3 atoms clustered together pump up their colour dramatically, sometimes to the extent that dealers have labelled the very best examples as ‘kryptonite’ diamonds.
A further unique colour range is occupied by olive diamonds. Never pure in colour by their very own definition these stones can either be a warm yellowish green or a cooler greyish green. Unlucky Brown may also be present. Olive is caused by nitrogen in isolated 1b and aggregate 1b form and/or combined with hydrogen (grey) vacancy defects. This arrangement of impurities leads to selective absorption in the violet to the blue and red part of the visible light spectrum respectively. Olive diamonds are also commonly fluorescent.
Countries known to be regular sources of pleasant green diamonds particularly include Brazil, Venezuela, Angola and Liberia.