Moving mountains for you
Switch currency

Current Live Auctions

Current Live Fixed Price Sales

Aenigmatite With Elpidite Molybdenite & Gaidonnayite

Views:
Watches:
LMB549559

Aenigmatite With Elpidite Molybdenite & Gaidonnayite

Analysed

Description Tabs

Description
Locality: 
Mont Saint-Hilaire, Montérégie, Québec, Canada
Class: 
Crystals on Matrix
Size Range: 
Small miniature (3-4.5 cm)
Size: 
3 × 3.5 × 2.5 cm
Weight: 
45.00gr
Description

Aenigmatite is a very rare mineral at MSH. According to a brief notice in the November 2011 CMMA “Micronews” (p. 5), only two finds had been reported up to that time. This specimen is not from either of those finds. Instead, it is from the Poudrette pegmatite “complex”, and is associated with a much greater variety of minerals including elpidite, gaidonnayite, lorenzenite, fluorapatite, molybdenite,  dark amphibole, dark mica (probably annite), and at least two unidentified phases. The matrix is “feldspar”.  The specimen is not from the pegmatite proper, but I am not sure exactly how to label the environment. In some ways, it is like a breccia.

The ID is based on qualitative EDS and visual appearance. To be certain that it is aenigmatite, PXRD and/or WDS would be required. Both cost $$. However, there a several observations which make the ID at least plausible. I have put these observations at the end of the description because they may be more than most people care to slog through.

The first photo (FOV 3.7 x 2.4 mm) shows all of the radiating aenigmatite on the specimen. The individual crystals are <= 1.9 mm. The reddish-brown color appears to be typical for aenigmatite at MSH, and is what prompted the analysis.

However, the perceived color depends on illumination etc. In the next photo (FOV 2.4 x 3.5 mm), the aenigmatite appears much more brown.

The next pair of photos (FOV 3.2 x 2.4 mm)  shows the main molybdenite crystal (2.9 mm) on the specimen. Yes, this is a very crumpled crystal of molybdenite. But that's the point. I know I'm a sloppy collector, but every molybdenite crystal from this find (on other specimens), even ones hidden deep inside little cavities, appears to be crumpled. I know that molybdenite is flexible, but I don't think I was the guilty party here. Why does it do that?

Regarding the color: In reality, the molybdenite has the usual bright silvery hue with blue highlights. But, because of the specular reflections, only rarely am I able to show that in a photo. Most of my photos make the molybdenite look black & white.

The next pair of photos (FOV 4.4 x 6.4 mm) shows some of the elpidite (3 mm) and gaidonnayite (0.35 mm) on the specimen. The elpidite is quite lustrous and mostly well terminated. The gaidonnayite crystals are tiny, but colorless and well formed. With a good scope, they can look beautiful. Note also the little dark gray-green blobs on the elpidite. They consist of tiny thin plates of an unidentified mineral (possibly catapleiite). There are two other elpidite sprays and many gaidonnayite crystals on the specimen.

The next photo (FOV FOV 5.4 x 4.2 mm) shows one of the other elpidite sprays (ca 2.7 mm).

The next pair of photos (FOV 1.25 x 1.55 mm) is an extreme close-up of two of the gaidonnayite crystals. They are very small (0.25 mm), but very sharply formed. The somewhat “bronzy” needles are probably lorenzenite, rather than aegirine or an amphibole. (Similar needles on another specimen found the same day were verified as lorenzenite via EDS.) The darker, more robust, prisms are an amphibole. The optics on my scope are not really suitable for photographing such small objects. I had to do a lot of Photoshop editing.

The fluorapatite consists of tiny, water-clear, sharply formed prisms. The “annite” consists of embedded anhedral plates. These are just accessories. I did not attempt to photograph them.

Now, regarding the ID:

Firstly, the EDS scan shows the presence of Fe, Ti, Si, and Na plus a minor Mn peak. (See the “Analysis” tab.) The Na peak may seem insignificant, but Na is difficult to detect, especially with this equipment.  To make it clear just how difficult, I have included a scan for “known” aegirine. Note that, even though the ideal formula for aegirine has one atom of Na for every atom of Fe (NaFeSi2O6), the Na peak is puny compared to Fe. For aenigmatite, the ideal formula has 2.5 atoms of Fe for every atom of Fe (Na2Fe5Ti[Si6O18]O2), so it is not surprising that the Na peak in the aenigmatite scan looks even more insignificant.  

Note also that, while the ideal formula for aegirine has 2 atoms of Si for every atom of Fe, the Fe and Si peaks in the aegirine scan have about the same height. Again, that is because Si is detected less readily than Fe. In this case, it appears that Fe is detected about twice as easily. While it is not really possible to “calibrate” a qualitative EDS scan – there are too many other variables which can affect relative peak height – if we foolishly extrapolate this result to the aenigmatite scan, we might expect that the Si peak there will be perhaps half as high as the Fe peak. That is, in fact what was observed.

Furthermore, the Fe peak (above noise) is about 4 times as high as the Ti peak, which is close to what one might expect for aenigmatite (taking into account that Ti is even easier to detect than Fe). (‘Titanian-aegirine’, a variety of aegerine, can have significant amounts of Ti. I have included a scan for an example. Note that Fe and Si still have similar peak heights, as opposed to what is seen in the aenigmatite scan.) 

Secondly, while the above discussion doesn’t actually prove anything, it does imply that the Ti in the scan is probably “essential”. If one then searches for all minerals with essential Na, Fe, Si, Ti (and O) and “optional” Mn, one gets a short list of 6  named and 3 unnamed minerals. Only two of these, aenigmatite and narsarsukite, have been reported from MSH. Clearly this isn’t narsarsukite! As for the others, they are easily eliminated based on appearance and hardness (e.g. nalivkinite is an astrophyllite group mineral and nafertisite which is closely related to the astrophyllite group) or chemical formulas that deviate too far from that of aenigmatite (which, modulo the fact that one isn’t “supposed to”  compare peak heights, I have just shown to be a good fit for the EDS scan).

In any case, unless you can find an MSH aenigmatite specimen that has been verified via PXRD and/or WDS, this is about as verified as it gets.

Single item shipping weight (no case) is 4.2 oz (87 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 (ca $9.25 including packing – varies by destination). 

Mineral Data
What's on the rock

Aenigmatite

Formula: 
Na2Fe2+5Ti(Si6O18)O2
Strunz: 
9.DH.40
Crystal System: 
Triclinic
Hardness: 
5.5 - 6.0
Type Locality: 
Kangerluarsuk Fjord (Kangerdluarssuq Fjord), Ilímaussaq complex, Narsaq, Kujalleq, Greenland

Elpidite

Formula: 
Na2ZrSi6O15·3H2O
Strunz: 
9.DG.65
Crystal System: 
Orthorhombic
Hardness: 
5.0

Molybdenite

Formula: 
MoS2
Strunz: 
2.EA.30
Crystal System: 
Hexagonal
Hardness: 
1.0 - 1.5

Gaidonnayite

Formula: 
Na2Zr(Si3O9)·2H2O
Strunz: 
9.DM.15
Crystal System: 
Orthorhombic
Hardness: 
5.0 - 0.0
Streak: 
White
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
Analysis
Analysis Report - only: Aenigmatite With Elpidite Molybdenite & Gaidonnayite
LMB minerals

Seller Information

Payment options: offline, paypal_wpp, paypal_wps

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.