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PhotosAfghanite - Ladjuar Medam, Sar-e Sang, Koksha Valley, Khash & Kuran Wa Munjan Districts, Badakhshan Province, Afghanistan

19th Jun 2017 23:21 UTCRichard Gunter Expert

Afghanite

Sar-e-Sang, Kuran wa Munjan District, Badakhshan, Afghanistan

Are you certain this is Afghanite? Green Hauyne can have the same fluorescent colours as Afghanite and these look more like dodecahedral crystals than hexagonal crystals.

19th Jun 2017 23:46 UTCRob Woodside 🌟 Manager

I think this is hexagonal, but looks like no afghanite I've seen. It is probably worth analysing. The sodalite minerals (Sodalite, Nosean, Hauyne) all come from Afghanistan, but so far only one of the two dozen Cancrinite minerals (Afghanite) is reported from Afghanistan.

21st Jun 2017 11:56 UTCAxel Emmermann

These afghanite enigmas boil down to the mineral being composed of layers of different minerals (cancrinite, liottite, sodalite...) Crystals can be hard to recognize just by looking at them. If afganite fluoresces, which it quite often does, you'll see the typical vibronic spectral peaks of disulfide. These disulfide ions are locked in the aluminosilicate cages that are formed in these type of minerals. The distance between these peaks and the position of their larger "enveloping" peak is a function of the size of these cages. In the case of afghanite, there are several DIFFERENT cage sizes, so you tend to get two effects:

1) the peaks are slightly assymetrical

2) the peaks shift slightly to the blue if you measure the emission along the c-axis of the crystal and slightly to the red if you measure along the a-axis (any of those three.)

It is a bit weird but it allows you to identify afghanite from other cancrinite-sodalite family members.

21st Jun 2017 14:30 UTCJosé Zendrera 🌟 Manager

Crystals are hexagonal, no doubt, but pyramidal faces in many orders (until 5) and the pinacoidal face at termination gives them a weird aspect.

Another strange thing: The whole piece has a parallel color zoning (transparent/white) which goes across the four crystals of the sample, as can be seen in following picture.

Could it be a pseudomorph?

Thanks for your opinion.

23rd Jun 2017 20:56 UTCReiner Mielke Expert

I'd say the zoning is due to healed fractures.

23rd Jun 2017 22:27 UTCRob Woodside 🌟 Manager

Interesting zoning that is typical in sodalites! from the Richterite occurrence. One might think that they might be healed cleavages, but the two xls don't look like twins, so I think Reiner has it.

Don Newsome has an Ocean Optics machine and he kindly used it to show me the luminescence spectra of some of these minerals. What struck me was the similarity of these emission spectra and the Raman spectra I had been finding in Bob Down's Lab. In Don's case we were using Don's UV lights and in Bob's case we were blasting them with intense green or red laser light. Sometimes the spectra would be just a large hump and in other cases it looked like a Stagasaurus with equally spaced spikes above the hump. I had always wondered why there should be such a broad hump? The "spikes' which themselves were fairly broad looked like vibrational spectra are are probably the S₂^-1 that Axel refers to. If you cooled a specimen that had only a broad hump would the spikes start appearing as it cooled? Relating cage dimensions to luminescence is really interesting! Is there anything published on this?

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