Explaining the ‘chameleon’ phenomenon
The presence of hydrogen and nickel in chameleon diamonds has been demonstrated by various spectroscopic methods—emissions assigned to nickel impurities were identified by PL spectroscopy, particularly in the classic group. At present, we can only speculate these two impurities are the cause of the colour change exhibited by classic chameleon diamonds.
The results point to a defect involving hydrogen that could be detected with an infrared spectrometer combined with the 480nm band (related to isolated single nitrogen atoms) detected using a visible spectrometer.
This combination seems to cause the thermochromic and photochromic change in colour, but whether or not nickel plays a role in colour change remains to be seen. In the diamonds exhibiting only a thermochromic colour change (i.e. reverse chameleons), the defects appear to be solely hydrogen-related.
Sources of chameleon diamonds
It is difficult to definitively prove the origin of chameleon diamonds based on testing, but mines located in the Central African Republic produce a good percentage of classic chameleons, while Rio Tinto’s Argyle may be one source of reverse chameleons, which are rich in hydrogen.
