Afghanite: a beautiful rarity

Named after the country where it was found and the main locality for the lovely gemmy blue crystals like the one in the photo, it is a metamorphic mineral, born in the crushing heat and pressure of the ongoing mountain building event that is upthrusting the Himalaya, Hindu Kush, Altai, Pamirs etc into contorted folds of squished transformed rock. It was first discovered in 1968 in the Lapis Lazuli mine of Sar-e-Sang, Badakhshan Province where it cuts veins of another blue mineral called lazurite, which remains the main locality. It formed as sea bottom limestones turned into marble.

Colours include colourless and yellow alongside these vivid blues, and the hardness is medium at 5.5-6 on Mohs scale, the same as feldspars. The mineral glows bright orange in UV light, as electrons are excited by the energy, jumping up a level and giving off the energy as visible light as they fall back down. Other sources include Germany, Italy and Siberia. The specimen in the photo (4.2 x 3.8 x 3.7 cm) is Afghan.


Image credit: Joe Budd/Rob Lavinsky/iRocks.com



Australia’s Argyle diamonds are naturally pink in colour, though why has been a mystery to scientists for quite some time. New research into the photochromic behaviour of Argyle diamonds (the way diamonds change colour upon exposure to light) led by Keal Byrne, a PhD student at the University of Western Australia in Perth, has taken a step towards determining what creates this colouration. Byrne and his team used a suite of lights with narrow frequencies to bleach the colour from the pink diamonds, which allowed them to understand their photochromic behaviour.

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