Properties and Colouration of Orange Hackmanite from Afghanistan
Since the latter half of 2023, yellow-orange to deep orange hackmanite from Badakhshan, Afghanistan, has appeared on the gem market.
Eight faceted samples were examined for this report that were light yellowish orange to strong orange, and exposure to UV radiation caused them to become pinkish orange to orangey red.
The addition of a purple colour component due to UV exposure is consistent with the photochromism typically observed in hackmanite.
An absorption band at 480 nm is responsible for the orange hue, but it does not correspond to any other known colour centre in the sodalite structure.
The presence of unaltered two- and three-phase fluid inclusions suggests that the samples had not been heated.
Repeated exposure to UV radiation eventually causes the stable colour to fade (to light orangey yellow) and also diminishes the photochromic behavior, so we conclude that the 480 nm band is most likely due to irradiation, which could be natural, artificial or both.
Irradiation experiments performed on faded samples prove that the unstable deep orange colour, as well as the photochromic behaviour, can be temporarily restored by exposure to 150 kGy of gamma-ray radiation.
- Féodor Blumentritt, GGTL Laboratories Switzerland
- Franck Notari, GGTL Laboratories Switzerland
- Candice Caplan, GGTL Laboratories Switzerland
Read the full article in The Journal of Gemmology
The Journal of Gemmology, 2024, Volume 39, n° 2, pp. 160-170.