This is complex specimen, probably from a sodalite xenolith. The main minerals of interest are thermonatrite (with a bit of etched villiaumite), vuonnemite, and “eudialyte group” (perhaps one of the kentbrooksites or plain eudialyte). In addition, there are numerous small, colorless, fluorapatitep prisms and minor pectolite and aegirine. Several of these minerals were analyzed. (See the “Analysis” tab.)
Some of the thermonatrite and villiaumite is shown in the first pair of photos (FOV 3.6 x 2.3 mm). The villiaumite (far right) appears to be an etched cubic crystal. But villiaumite cleavage fragments are hard to distinguish from real crystals. There is another, similar, cavity with thermonatrite and viliaumite nearby. There is not a lot of thermonatrite (or villiaumite) on the specimen, but it is a very rare mineral at MSH.
The second pair of photos (FOV 5.0 x 4. 1 mm) shows the largest and best “eudialyte” crystal on the specimen. The colorless prisms are mostly fluorapatite. The “eudialyte” was analyzed via qualitative EDS and the analyst tentatively suggested “kentbrooksite”, probably on account of the presence of Ce. However, there seems to be more Fe than Mn, which might make this ferrokentbrooksite (assuming that all of the Fe is concentrated in a single site). Also, when Nb is present (as it should be for the kentbrooksites), the Zr peak typically develops a secondary bump on the right shoulder, and I don’t really see that in the scan. So this could just be plain eudialyte (which sometimes also has REE). All of this just illustrates the folly of attempting to ID EGMs via qualitative EDS. But the exercise is not totally useless. I can say with some confidence that it is not johnsenite-(Ce) or one of the khomyakovites, and probably not zirsilite-(Ce) or oneillite.
The next pair of photos (FOV 2.2 x 2.9 mm) shows two more “eudialyte” crystals and a bit of pectolite (bottom right). The pale yellow flakes are actually vuonnemite. See scan #260. All of the yellowish stuff seen in the full-view photo is vuonnemite. It is apparently unaltered, but all of it consists of just very small, jumbled, plates, and there is little if any SW UV response.
The next pair of photos (FOV 2.3 x 3.7 mm) shows some of the fluorapatite (top) and a K-feldspar, probably microcline. (Sanidine does not occur in the sodalite xenoliths). The apatite crystals are <= 0.6 mm long. The next photo (FOV 1.3 x 1.7 mm) is a close-up of some of tem. EDS shows the presence of some REE.
Single item shipping weight (no case) is 3.5 oz (100 g). For shipments outside the USA, up to a total weight < 8 oz (225g), this can be combined with items from this or other auctions for the same postage.
Within the USA, postage increases by about $0.20 per ounce. Above 13 oz, I will use Priority Mail (about $9.25 including packing – varies by destination).
