Chameleon Diamonds

(via Wahroongai News, Volume 32, Number 4, April 1998)

Chameleon diamonds are rare hydrogen-rich diamonds that change color when exposed to heat. The most famous named chameleon diamond is the 22.28 ct heat-shaped Green Chameleon diamond—a diamond that changes color from grayish green to bright yellow under one of two circumstances.

Heat the green (stable color) chameleon diamond in the flame of an alcohol lamp to a temperature of 200 – 300ºC and its color will convert to an unstable bright yellow. Overheating to ~ 500ºC. If the unstable yellow colored chameleon diamond is in the dark for 24 of more hours, within a few minutes of its removal form the warm darkness its color will revert from unstable bright yellow to stable green color which is caused by the absorption of UV wavelengths from visible light.

The cause of this chameleon effect is an extremely broad absorption extending from ~ 550nm into the infrared, leaving a green window in the visible. Green chameleon diamonds also display characteristic greenish yellow phosphorescence to LWUV, which may last for several minutes after irradiation ceases.

Over recent years at least two other chameleon-type diamonds have been discovered:
-The first group is some pink Argyle diamonds that briefly change to brownish pink when subjected to strong UV irradiation
-The second group is a single specimen that changes from faint pink to colorless after UV irradiation. Gentle heating returns the faint pink color to this diamond. When exposed to UV light this chameleon has a strong apricot pink fluorescence, but a protracted yellowish green phosphorescence to follow.