“Originally posted as "UK galssy prisms": "too galssy to be elpidite", but "doesn’t look like nenadkevichite". Update Dec 2020: Recent higher quality EDS clearly suggests "nenadkevichite". See the new analysis child photo. Now obsolete: September 2017: A sample has now been analyzede via qualitaive EDS, which indicates something intermediate between korobisynite and nenadkevichite. In fact, the Ti peak is substantially higher than the Nb peak, which suggests korobitsynite (or Tsepinite-Na, its monoclinic relative.) But Ti is more easily detected than Nb and, in any case, comparison of peak heights in qualitative EDS scans can be very misleading. (In this case, it certainly is very tempting. See the analysis "child" photo.) This specimen was found in July 2002 in material from the Poudrette pegmatite complex.”

“This is a stereo child photo.”

“Update Dec 2020: Recent higher quality EDS clearly indicates Nb > Ti - i.e. nenadkevichite Original description: Qualitaive EDS indicates something intermediate between korobisynite and nenadkevichite. In fact, the Ti peak is substantially higher than the Nb peak, which suggests korobitsynite (or Tsepinite-Na, its monoclinic relative.) But Ti is more easily detected than Nb and, in any case, comparison of peak heights in qualitative EDS scans can be very misleading. ”

“This is a stereo child photo showing a nearby part of the cavity. ”

“This is an extreme close-up attempting to show that the crystals look orthorhombic. But the photo isn't very sharp so I'm not sure that that is very clear. In any case, monoclinic crystals could mimic this shape just as well. The only way to be sure would be XRD/ Note: At high magnification, my scope degenerates into one big chromatic abberation. By the time that I "fix" that, this is about as sharp as I can make the photos - i.e. not very. Viewing the images in stereo does help. ”

“This is a stereo child photo. It attempts to show that the crystals are orthorhombic. But the image isn't clear enough, and, in any case, only XRD can tell for sure. The crystal in the center appears to be a "sort of" scepter. The total length is 0.85 mm. The thicker top part is 0.65 mm long.”

“Update Dec 2020: Recent, higher quality EDS (thanks to Joy Desor), shows that Nb is atually significantly more abundant than Ti ca 8:3). Overall, the scan is a very good fit for nenadkevichite with about half of the Na site being vacant. See the new child analysis photo for details. I have left the previous description as first posted so that you can see how treacherous it can be to ID labuntsovite group minerals - even with analytical data. Original description: This could be korobitsyinite, tsepinite-Na - or just plain old nenadkevichite. Qualitative EDS shows a Ti peak substantially higher than the Nb peak. Taken literally, that would imply korobitsynite or tsepinite-Na (which are chemically identical). But qualitative EDS can be misleading becuase Ti is detected more readily than Nb and because peak heights can depend on other factors besides the chemical composition. In my own little world, I think this is korobitsynite, but I have posted it very conservatively here as "labuntsovite supergroup". Only WDS + XRD could say for sure. Not in my budget. See the analysis "related" photo for the EDS scan.”

“This is EDS data - not WDS. But it seems pretty clear that Nb >> Ti - rather than Ti >> Nb as was suggested by the initial quick and dirty EDS scan. While the "quantitaive" data that accompanies the scan has to be taken with a very large grain of salt - way too many decimal places - it appears to be an excellent mach for typical MSH nenadkevichite (with about half the Na sites being vacant): Element Wt % At % NaK 15.43 26.57 AlK 0.58 0.85 SiK 34.37 48.45 ZrL 4.60 2.00 NbL 37.67 16.06 TiK 7.34 6.07 The only thing unusual is the Zr. ”