[Rockhounds] Scapolite again

Fri Oct 3 11:43:10 PDT 2008

Hi Pete, (and scapolite worshippers at large),

This text seemed a little outside the scope of what I was looking for
somehow.
But then I found that it may indeed be significant in another aspect...
If I understand it correctly, Antao and Hassan performed some kind of
annealing on the sample by heating and cooling it. 
Would this logic apply? : If T1 sites become fully ordered (with predominant
Si) and T2 sites fully disordered (about equal Si and Al), the anion cage
would become more oval shaped (since the length of Al-O bonds differ from
Si-O bonds). I suppose that this would cause a shift in what fits in best...
carbonate or sulphate instead of Na4Cl(-3)
It would also look like (my laymen's interpretation ;-))) that annealing
over long geological periods would permanently differentiate the Al and Si
in the structure so that the T1-sites become virtually pure SiO4 while the
T2 sites become highly ordered alternating SiO4-AlO4 rings. 
I don't see a direct connection with what I'm looking for but I would be
inclined to think that it might be rewarding to compare meionite specimens
coming from really big, slow cooling intrusions with those from smaller
metamorphic regions.

Thanks for the link
Axel

> -----Oorspronkelijk bericht-----
> Van: rockhounds-bounces at lists.drizzle.com
[mailto:rockhounds-bounces at lists.drizzle.com]
> Namens pmodreski at aol.com
> Verzonden: woensdag 1 oktober 2008 20:03
> Aan: rockhounds at lists.drizzle.com
> Onderwerp: Re: [Rockhounds] Scapolite again
> 
> Hi to Axel & the others (in case anybody still does care more about
"scapolite"),
> 
> At the risk of repeating info that may already have been mentioned here
(without reading
> back over all the past posts on this topic),
> 
> I'm still thinking about scapolite off and on, so, Axel et al., were you
aware of the most
> recent paper about scapolite that appeared in American Mineralogist,
Aug-Sep 2008; the
> abstract is posted on the MSA website at,
> 
>
http://www.minsocam.org/MSA/ammin/toc/Abstracts/2008_Abstracts/AS08_Abstract
s/A
> ntao_p1470_08.pdf
> 
> Unusual Al-Si ordering in calcic scapolite, Me79.6, with increasing
temperature, by Sytle M.
> Antao and Ishmael Hassan
> 
> 
> Reading it reminded me, among other things, that the sulfate end-member of
the scapolite
> group HAS been officially described as a separate mineral species,
silvialite.? That name was
> used much earlier (1914, according to Mindat.org) for the hypothetical
sulfate scapolite end-
> member, but it was officially approved in 1998, and published in 1999, for
the type locality
> being in Queensland, Australia.? Just two pictures of silvialite are
posted on the Mindat
> gallery, both from
> Loitsch Quarry, Weida, Gera, Thuringia, Germany
> 
> That's all for now!
> 
> Pete
> 
> 
> 
> 
> 
> 
> 
> 
> -----Original Message-----
> From: pmodreski at aol.com
> To: rockhounds at lists.drizzle.com
> Sent: Fri, 26 Sep 2008 9:50 am
> Subject: Re: [Rockhounds] Scapolite
> 
> 
> 
> 
> 
> 
> 
> "It's probably the same with series like calcite - rhodochrosite."
> 
> 
> Not quite the same situation, Axel, because with the carbonates,
relatively pure
> calcite is by far the most common, then with varying small amounts of
manganese
> making the manganoan calcite ("manganocalcite") varieties.? Then it's also
> complicated by the existence of the intermediate compound analogous to
dolomite,
> namely kutnohorite, CaMn(CO3)2 .? I believe that the special issue of Min.
> Record dedicated to the Sweet Home mine, July-August 1998, in the article
by
> Karen Wenrich, included a diagram or a table showing compositions of Sweet
Home
> rhodochrosite analyzed by microprobe, showing how the compositions are
> distributed as regards Ca vs. Mn content; and that the gemmy red
rhodochrosites
> were purest in Mn, and the paler, cloudy-pink ones contained more Ca.? I
don't
> have the issue at hand right now or I'd look this up and refresh myself as
to
> exactly what it shows.
> 
> Pete
> 
> -----Original Message-----
> From: Axel Emmermann <axel.emmermann at pandora.be>
> To: 'Rockhounds at drizzle.com: A mailing list for rock and gem collectors'
> <rockhounds at lists.drizzle.com>
> Sent: Fri, 26 Sep 2008 3:24 am
> Subject: RE: [Rockhounds] Scapolite
> 
> 
> 
> Hi Pete,
> 
> Thank you for sending the list.
> I guess the scapolite story is no different from most continuous series.
If
> you look at the results:
> 
> 0-20% meionite: 2 samples
> 20-40% meionite: 5 samples
> 40-60% meionite: 7 samples
> 60-80% meionite: 5 samples
> 80-100% meionite: 1 sample
> 
> Now that is a classical Gaussian bell curve if ever I saw one. ;-)))
> 
> It's probably the same with series like calcite - rhodochrosite.
> 
> Cheers
> Axel
> 
> 
> 
> > -----Oorspronkelijk bericht-----
> > Van: rockhounds-bounces at lists.drizzle.com
> [mailto:rockhounds-bounces at lists.drizzle.com]
> > Namens pmodreski at aol.com
> > Verzonden: donderdag 25 september 2008 22:34
> > Aan: rockhounds at lists.drizzle.com
> > Onderwerp: Re: [Rockhounds] Scapolite
> >
> > (OK, anybody tired of hearing about scapolite, just delete this!)
> >
> > A little more data, for Axel & all,
> >
> 
> > (1) I looked through my files and found a good article, by Teertstra &
> Sherriff, 1996, Am.
> > Min. v. 81, 169-180 (it should be online too, via the MSA website),
which
> gives complete
> > chemical analyses, and other (XRD, etc.) data, for some 20 scapolite
> samples from around the
> > world.? For my own interest I typed out a list of the 20 localities and
> their composition in
> > terms of % of the meionite (calcium) endmember--if anyone would like to
> see this, please just
> > write to me & I'll email it back to you.? But here is a quick summary of
> what it shows:
> >
> > 0-20% meionite: 2 samples (Pamirs, Russia, light violet gem crystal, and
> Gooderham, Ontairo,
> > opaque blue-gray)
> > 20-40% meionite: 5 samples (Quebec, Ontario, Tanzania, Brazil)
> > 40-60% meionite: 7 samples (Quebec, Ontario, New York, Madagascar,
> Tanzania)
> > 60-80% meionite: 5 samples (Quebec, Massachusetts, Russia (Slyudyanka)
> > 80-100% meionite: 1 sample (Monte Somma, Italy; 96.5% meionite)
> >
> > This article also mentioned that it used, as a standard for microprobe
> analysis, a "gem quality
> > meionite from Brazil, U.S. National Museum No. R6600-1", but it doesn't
> give the exact
> > composition of that specimen.
> >
> > (2) I see that there was also a pa
> per published, "On the composition of
> gem scapolites", by
> > Pete J. Dunn et al., 1978, Journal of Gemmology, v. 16, pp. 4-10.? I
don't
> have a copy of this
> > paper now, but I'm requesting one via our library.
> >
> > (3) The mention above of the USNM meionite gave me the idea of checking
> the U.S. National
> > Museum of Natural History's (Smithsonian Institute) catalog, which is
> searchable online--it
> > is at,
> > http://nhb-acsmith1.si.edu/emuwebmsweb/pages/nmnh/ms/Query.php
> > The result is interesting--I searched according to what mineral name
> specimens are
> > catalogued under, which of course is subject to the same caveats
expressed
> here for Mindat
> > entries--yes, I agree, one doesn't know how accurate the "meionite vs.
> marialite" entries for
> > any of the specimens are, though one might hope that the Smithsonian
> catalog
> information is
> > more authoritative than most.? Here's what the catalog shows:
> >
> > "Scapolite" - 621 entries
> >
> > "Marialite" - 35 entries (including 8 from U.S., 6 Canada, 6 Tanzania, 3
> Madagascar, 1 Brazil,
> > 1 Mozambique)
> >
> > "Meionite" - 67 entries (including 25 "Vesuvio", 8 Brazil, 7 U.S., 6
> Canada, 2 Madagascar, 1
> > Tanzania, 1 Kenya, 1 Burma)
> >
> > "Wernerite" - 12 entries
> >
> > "Mizzonite" - 18 entries
> >
> > Of course, most of the Smithsonian specimens I'm sure have not been
> analyzed,?but just
> > catalogued under the mineral name by which they were received; hence,
the
> large number of
> > "just plain scapolite" entries.
> >
> > Pete
> 
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