This specimen features ”pyrochlore” and rhabdophane-(Ce), both with rather unusual compositions, as well a lorenzenite, which is an extremely rare mineral in the pegmatites at MSH. (Lorenzenite is found mostly in hornfels and igneous breccia here.) The lorenzenite is also unusual in that it is enriched in Nb.

“Pyrochlore” is uncommon but not rare at MSH. What makes the pyrochlore on this specimen unusual (apart from the yellow color), is the presence of very elevated levels of Si. (See scans #123 and #124 – for another specimen – under the “Analysis” tab. Apparently elevated levels of Si in pyrochlore are known from MSH (and elsewhere) but it is so unusual that the analyst was initially tricked into labeling the Si peaks as Ta. Since one of the scans showed “Ta” > Nb, this led to speculation that the mineral might be “microlite”, but that is not the case. It is merely very weird “pyrochlore” – probably weird fluorcalciopyrochlore. (Explanations for how the pyrochlore could contain so much Si vary. This is not the place to go into that.)

The pyrochlore group at MSH presently consists of fluorcalciopyrochlore and fluornatrolpyrochlore. In the EDS scans for the “pyrochlore”, Ca is very evident, but Na not at all – hence “fluorcalciopyrochlore”. So the fluorcalciopyrochlore ID is a best guess – but that’s as good as it is going to get unless you are willing to pay $$$ for WDS (and even that can suffer from Na “migration” under the electron beam).

FOV in the first pair of photos is 4.4 x 6.7 mm. The individual “pyrochlore” crystals are <= 0.25 mm. The dark prisms are aegirine, the background is albite.

The third photo (FOV 3.6 x 2.4) is a close-up of a different part of the specimen. At this higher magnification, the “pyrochlore” looks encrusted, and at least some of the crust is removed by soaking in HCl. But there isn’t any vigorous fizzing, and the EDS scan for the crust is similar to that for the “naked” crystals.

The specimen is very rich in “pyrochlore”. The areas shown are only a part of the coverage.

Rhabdophane-(Ce) is “medium rare” at MSH, and occurs only as pseudomorphs. The precursor is unknown, but may be a mineral related to mckelveyite-(Y). (In one bizarre case, analysis indicates rhabdophane replacing polylithionite!) . The “crystals” on this specimen are small, but well formed. But the most interesting thing about this find is that, as determined by microprobe (Pavel Kartashov – IGEM), they are very high in Ca – nearly brockite in composition. Brockite is extremely rare at MSH. (But this is NOT brockite. The composition of the “Ce site” was found to be ((Ce.28 La.16 Nd.07 Pr.03 Eu.01 Gd.01 Sm.01)sum=0.56 Ca.33 Sr.10 Ba.01)sum=1.00. So even though Ca is the single most abundant anion, the material is REE dominant, with Ce being the most abundant of the REE.) The rhabdophane is shown in the fourth and fifth photos. The rhabdophane is the little “mushrooms”. (They are actually hexagonal.) The thinner, white, platy stuff is a coating on “something”. It has not been identified, but is probably a mixture.

The next pair of photos (FOV 3.7 x 2.0 mm) shows the major concentration of lorenzenite. The individual crystals are <= 0.65 mm.

In the most recent special issues on MSH (Lapis and Rivista, 2000), lorenzenite at MSH is not listed as occurring in pegmatites. But this lorenzenite is clearly from an altered pegmatite and was verified via EDS on samples from two different specimens. (See the “Analysis” tab. Scan #166 – for this specimen - is a good fit for lorenzenite. Vinogradovite produces a similar scan, but the Si peak is higher relative to the Ti peak in that case. I have included scan #298X - from another specimen - for comparison.)

As mentioned, this is from an altered pegmatite. That means that there is a lot of “mineralogical dirt”. It may be possible to remove some of it, but probably not without also removing something of interest.

Single item shipping weight (no case) is 6.3 oz (179 g). For shipments outside the USA, up to a total weight < 8 oz (225g), this can be combined with a small item or two from this or other auctions for the same postage.

Within the USA, postage for total weights up to 13 oz, ranges from $4.50 to $6.50 (including packing etc) regardless of destination. Above 13 oz, I will use Priority Mail ($7.25 - $9.20 including packing – varies by destination).