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UV MineralsSelenite with triangular features that become visible in UV light (LW)

13th May 2017 23:26 UTCJason Evans

I have had these selenite crystals for a couple of years but it is only just 3 hours ago since i noticed a friend posted some photos of similar crystals which have these triangular "phantoms?" and out of curiosity I wondered if mine had the same effect, which they do. His selenite is from Willow creek, Alberta, Canada. My specimens did not come with the correct locality, in fact even the mineral species was incorrect, they were sold as calcite from Iceland, oops! I am wondering if this feature is unique to selenite from Willow creek that would help me to put a locality to my ones, but I suspect it's probably seen in selenite from many other localities.

14th May 2017 00:31 UTCSteve Hardinger 🌟 Expert

It's not quite unique to Willow Creek. I've seen the same fluorescence (albeit faintly) in gypsum from Kansas. However the perfection of the crystal and the brightness of the fluorescence strongly suggest Willow Creek.

These things are not rare (I own maybe ten and have seen hundreds over the years), but they don't show up as frequently as they did 20 years ago.

14th May 2017 01:56 UTCJason Evans

Thanks Steve, it was the perfection of the crystals that made me decide to buy them, i normally would not buy a mineral without locality info, but for £1 for 4 crystals I thought it was worth it! at least now i have some idea where they could be from, which is better than no idea at all!

14th May 2017 01:57 UTCJason Evans

This was with LW as well, apparently the florescence is even stronger with SW but I am still yet to get an SW light.

14th May 2017 03:11 UTCBen Grguric Expert

I documented identical sector fluorescence and phosphorescence in gypsum crystal from Mepal, Cambridgeshire in 1998 (Russell Society Journal). In those examples there was green phosphorescence for up to 5 seconds after the UV source was switched off.

14th May 2017 07:30 UTCVolker Betz 🌟 Expert

Fluorescent gypsum crystals are known since:

- Himmel, H.(1927): Gips von Wiesloch(Baden). Centralblatt für Mineralogie, Abt. A (1927), 342-349.

- Iwase, Ei-ichi (1936): Über die Verteilung des Lumineszenzträgers im Gipskristall. Bulletin of the Chemical Society of Japan 11, 475-479.

A famous German locati is:

https://www.mindat.org/loc-32054.html

Volker

15th May 2017 14:54 UTCEd Clopton 🌟 Expert

Some of the gypsum crystals I collected from a roadside near Newcastle, Nebraska (https://www.mindat.org/photo-599500.html show faint fluorescent hourglass sectors under UV. I imagine they form any time a gypsum crystal picks up the right impurities on its f(120) faces as it grows.

15th May 2017 19:09 UTCSteve Hardinger 🌟 Expert

I suspect -- although I have not seen any definitive proof -- that the impurities are traces of organic materials. Perhaps some day I'll smash up some of these X-fluorescence crystals, extract the organics, and figure out their chemical makeup. Or maybe someone has already done this and I haven't seen the paper.

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