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Bastnäsite-(Ce) Psm Petersenite-(Ce) With Donnayite-(Y)

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LMB660410

Bastnäsite-(Ce) Psm Petersenite-(Ce) With Donnayite-(Y)

Analyzed find
Pseudomorph

Description Tabs

Description
Locality: 
Poudrette Quarry, Mont Saint-Hilaire, Québec, Canada
Class: 
Crystals on Matrix
Size Range: 
Thumbnail (1-3cm)
Size: 
2.5 × 2 × 1.5 cm
Weight: 
10.00gr
Description

MSH is well known not only for its spectacular array of rare and well-formed minerals, it is also well known - perhaps notorious - for its wide range of amazing, but often perplexing, pseudomorphs. This is a very good example of pseudomorphs of bastnäsite-(Ce), probably with synchysite-(Ce), after petersenite-(Ce) from the famous Poudrette pegmatite. (See below for more on the ID.) What makes it good is the fact that the pseudomorphs are very sharply formed and many have excellent “terminations”. In addition, the pseudomorphs host small rosettes of an interesting donnayite group mineral of an unusual flat-tabular habit (rather than the more typical cone shaped crystals).

Pseudomorphs of synchysite-(Ce) after petersenite-(Ce) and/or rémondite-(Ce) were fairly common in the Poudrette pegmatite. See for example p. 57 of the Lapis special issue on MSH (July/Aug 2000) or p. 98 of “Minéraux du mont Saint-Hilaire” (ISBN 978-2-9814937-0-5). These pseudomorphs come in several sub-types. Perhaps the most common are the pale tan PSMs of synchysite-(Ce) after petersenite-(Ce). These have a very characteristic “swirly” surface texture, due to the synchysite being almost micaceous. The pseudomorphs on this specimen are of a less common type in which bastnäsite-(Ce) predominates. (See below for details.)

In some cases there is relict petersenite-Ce) (or rémondite-(Ce)). But in this case (as is most common) there is not. The interiors are honeycombed and partly hollow. So I can’t really be sure that the precursor was petersenite-(Ce) rather than rémondite-(Ce). However, despite having the same space group, these two minerals have fairly distinct habits at MSH, and the PSMs look as if they started out as petersenite-(Ce). But that’s just my best guess. Strictly speaking, these are PSMs after “burbankite family”.

Both the “donnayite group” and the PSMs were analyzed via qualitative EDS. The scan (#311) for the “donnayite” (on a similar specimen – see the “Analysis” tab) shows Sr > Ba, so given that the equipment is more sensitive to Ba than to Sr, this is probably more donnayite than mckelveyite (or ewaldite). But only WDS (plus XRD) could tell for sure. (There is also a lot of Ce and La, and the low-energy Y peak isn’t very evident. This might suggest intergrowth with synchysite-(Ce) – which is a common thing at MSH. However, the Y peak is just “hiding” under the Sr. I have included a high-voltage scan (#5b) for similar material from a nearby find which shows a clear Y peak at higher energy. As for the Ce and La – they seem to be a common feature of EDS scan for “donnayite” group at MSH. Another indication that there is little if any synchysite mixed in is the relatively low Ca peak.)

EDS scans for similar specimens have shown scans intermediate between synchysite-(Ce) and parisite-(Ce). XRD on another specimen showed parisite-(Ce). I have included the scan (#365) for an even more similar specimen.

For that specimen, the sample was prepared by first removing soluble carbonates (such as synchysite-(Ce)) with dilute HCl. The resulting EDS scan shows a spectrum that is intermediate between bastnäsite-(Ce), and parisite-(Ce), but closer to bastnäsite-(Ce). (There is also residual Cl from the HCl.)  Since part of the sample dissolved more or less rapidly, probably synchysite-(Ce) was also present. (Bastnäsite-(Ce) and parisite-(Ce) are fluoro-carbonates and are soluble only with difficulty.)

The first pair of photos (FOV6.9 x 4.5 mm) shows several of the “terminated” PSMs and a much larger PSM whose “terminations’ ran into other stuff. Also visible are several “rosettes” of platy “donnayite”. The white crystal is albite.

The second pair of photos (FOV 4.3 x 6.6 mm) provides a different point of view showing more of the terminated crystals.

The third pair of photos (FOV 2.0 x 1.4 mm) is an extreme close-up showing a small, “terminated”, PSM with two of the best “donnayite” rosettes attached. The larger rosette is ca 0.35 mm in diameter.

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 for total weights up to 13 oz, ranges from $4.25 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).

Mineral Data
What's on the rock

Bastnäsite-(Ce)

Formula: 
(Ce,La)(CO3)F
Strunz: 
5.BD.20a
Crystal System: 
Hexagonal
Hardness: 
4.0 - 4.5
Type Locality: 
Bastnäs mines, Riddarhyttan, Skinnskatteberg, Västmanland, Sweden

Petersenite-(Ce)

Formula: 
Na4(Ce,La,Nd)2(CO3)5
Strunz: 
5.AD.15
Crystal System: 
Monoclinic
Hardness: 
3.0
Type Locality: 
Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry; Carrière Mont Saint-Hilaire), Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada

Donnayite-(Y)

Formula: 
NaCaSr3Y(CO3)6·3H2O
Strunz: 
5.CC.05
Hardness: 
3.0
Type Locality: 
Poudrette quarry (Demix quarry; Uni-Mix quarry; Desourdy quarry; Carrière Mont Saint-Hilaire), Mont Saint-Hilaire, La Vallée-du-Richelieu RCM, Montérégie, Québec, Canada
LMB minerals

Seller Information

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Seller's terms and conditions

In addition to the standard terms and conditions, please note the following. Almost all IDs are visual. While in most cases the ID is obvious, there may be cases where it is not. If you are doubtful about a particular ID, please ask for more information. Or do not bid! Similarly, if you are not sure that the specimen meets your criteria, do not bid. I have tdone the best I can with the photos. Nevertheless, if you are not happy with a specimen for any reason, I will refund the bid price – but not the shipping costs (unless the fault is clearly mine) – if the specimen is returned. This policy applies even if analysis of the specimen shows that my ID was incorrect. When in doubt, ask - or don’t bid. Note that most crystals at MSH and Varennes are micros - even if on large specimens. Please pay attention to the stated sizes. Any customs duties, fees etc. are the responsibility of the buyer.