Chamaeleon diamonds, as their name suggests, may change colour temporarily. These unique diamonds – a collector’s favourite – typically either shift from a greenish yellowish Grey or an olive Green to either a yellowish Green, bright Yellow or a striking orangy Yellow. More uncommon are stones changing from a lighter pink to colourless or brown hue such as are known from the Argyle Mine in Australia’s Kimberley region.
Some chamaeleon diamonds also exhibit a change of colour in reverse order. Colour change in diamonds is caused by exceptional Phosphorescence or ‘afterglow’ which slowly fades away. This effect is also rarely seen in otherwise pure hued intense, vivid or deep yellow stones which may display for minutes to hours a brownish tinge after having been subjected to a UV lamp. However, phosphorescence is not to be confused with the typical white fluorescence Chamaeleon diamonds also commonly display.
It is not yet fully understood which colour centres lie at the heart of this phenomenon. However, virtually all known Chamaeleon diamonds are classified as distinctly hydrogen-rich Type 1aA diamonds. At least the main green colour component is seen in many chamaleons, just like in other green diamonds, is proven to be caused by natural radiation damage experienced by the crystal.
To display a colour shift Chamaeleon diamonds need to undergo what physicists call an energy charge transfer via means of a catalyst. This is best achieved by cooling or heating diamonds if they are heat responsive. Such ‘thermochromic’ stones may be scientifically be distinguished by marked near infrared absorption. On the other hand, should a Chamaeleon diamond belong to the ‘light-sensitive’ or ‘photochromic’ type it is going to exhibit a change of hue in reverse order. This can be best experienced when such specimens are subjected to either UV or other light radiation or when removed from prolonged storage in darkness.
The rarest, costliest and most aesthetically appealing Chamaleon diamonds show a crisp olive green colour in daylight. In the case of reverse chamaeleons, a clear orange hue is the most preferred. Brownish secondary hues, though common, are generally less desirable.
Chamaeleons occur at all levels of saturation from GIA Fancy Light to Deep.
Most Chamalaeon diamonds originate from mines across Africa.