[Rockhounds] Scapolite and kutnohorite

Fri Sep 26 11:42:00 PDT 2008

Absolutely, Pete.
I meant something like one mineral going through a continuous series of
intermediates to arrive at the other end of the series.
I found the paper that Kreigh sent me very interesting in that respect.
Calcite-rhodochrosite is much simpler in terms of composition and structure
that of scapolite. 

Could antiphase domains mean something like the perthite/anorthite
exsolution but more on a molecular very local scale (and without the
exsolution ;-))). Something like a "zoning" of Ca and CO3 versus Na And Cl
over the distance of a few unit cells? 
If I read the paper correctly, the scapolite series "jumps" (or at least:
accelerates)  towards the meionite end when the Al/(Al+Si) ratio exceeds
0.35.  Would that explain why the "mean  composition" of scapolite is just a
little biased towards meionite?

Another side question: is kutnohorite more than just a randomly chosen point
on the calcite to rhodochrosite series? Is it structurally different? There
is some argument about a Belgian actually producing specimens of kutnohorite
instead of manganoan calcite. I believe that the argument lies in an
infrared spectrum. Is that possible?

Cheers
Axel

> -----Oorspronkelijk bericht-----
> Van: rockhounds-bounces at lists.drizzle.com
[mailto:rockhounds-bounces at lists.drizzle.com]
> Namens pmodreski at aol.com
> Verzonden: vrijdag 26 september 2008 17:51
> Aan: rockhounds at lists.drizzle.com
> Onderwerp: 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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