This specimen features very unusual “rosettes” of a donnayite group mineral on an unusual pseudomorph of (probable) synchysite-(Ce) after (probable) petersenite-(Ce). What’s unusual is that the “donnayite” looks very similar to arisite-(Ce) from MSH. However, the environment (Poudrette pegmatite) is different and qualitative EDS shows that the rosettes are most likely intermediate donnayite/mckelveyite-(Y) (or perhaps an inter-growth). See the “Analysis’ tab. Because the Sr peak is higher than the Ba peak despite the equipment being more sensitive to Ba, this is probably closer to donnayite than to mckelveyite (or ewaldite) . (MSH is the TL for donnayite-(Y).) But qualitative EDS scans can be misleading. To be sure, WDS ($$$) would be needed.
Also unusual is the appearance of the pseudomorph. Pseudomorphs of synchysite-(Ce) after petersenite-(Ce) (and/or rémondite-(Ce)) were locally abundant in the Poudrette pegmatite, but are usually pale tan in color and have a characteristic “swirly” surface (due to embedded micaceous flakes of synchysite). (See Lapis July/August 2000 p.57.) However, greenish and blueish PSMs with a “warty” surface, similar to the one on this specimen, have also turned out to be synchysite-(Ce) (in some cases possibly inter-grown with parisite-(Ce). (This specimen was not analyzed.)
As a bonus, the specimen also has a couple of small blue sodalite crsystals
Regarding the EDS scan: Because the equipment used is more sensitive to Ba than to Sr, the “donnayite” is probably closer to donnayite-(Y) than to Mckelveyite-(Y). But qualitative EDS scans can be misleading. One experienced analysis thought that Mckelveyite-(Y) was more likely. Only WDS ($$$) can tell for sure. (XRD might be needed to eliminate ewaldite as another possibility.)
The first pair of photos (FOV 4.2 x 6.85 mm) shows most of the “donnayite” rosettes (to 0.7 mm) as well as a good part of the synchysite PSM. Note the green “warty” texture near the termination. No attempt was made to ID the source of the green color, but some synchysite PSMs on a specimen from another find, with similar “warty” texture, were found to have small masses of powdery bright green ferroceladonite in their hollow interiors.
The second pair of photos (FOV 5.5 x 4.3 mm), is another view of the “donnayite” and underlying green “warts”.
The third pair of photos (FOV 4.4 x 5.55 mm) shows the blue sodalite. The top crystal is 2.9 mm wide. The crystals are fairly well formed, but somewhat rounded.
Single item shipping weight (no case) is 4.3 oz (122 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 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 “own box” Priority Mail. The rate, including packing, varies by destination from $7.25 to $9.50.
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