All, 9/27/01
I am relaying this message to the Geo-metamorphism List at
the request of my colleague Darby Dyar. If any of you are able to
help her find the desired Fe-rich feldspars, please contact her
directly.
Many thanks, Charlie
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------- Forwarded message follows -------
From: "M. Darby Dyar" <[log in to unmask]>
To: <[log in to unmask]>
Subject: Fe-rich feldspars
Date sent: Thu, 27 Sep 2001 11:01:45 -0400
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Dear colleagues,
I am looking for a few good Fe-rich feldspars!
We have recently begun successfully analyzing Fe valence state in feldspar
using a specially-configured Mossbauer spectrometer, although the duration
of these experiments is still LONG because the amount of Fe present is
usually so small. Furthermore, the resultant peak areas are difficult to
interpret because the ferrous and ferric iron atoms in the structure are
expected to have very different amounts of recoil, and thus the peak areas
do not directly reflect the amount of the species present. To determine the
recoil-free fraction for each of the different Fe valences, it is necessary
to take a single sample and run it at several (>20) different temperatures,
because the change in Mossbauer parameters with temperature is a function of
the amount of recoil. For such experiments, data quality and run times
improve dramatically as the total FeO content of the feldspar increases.
I am currently undertaking the task of determining the recoil-free
fraction of ferric and ferrous iron in feldspar, but this work would be made
much easier if I had a very iron-rich feldspar (i.e. >1.0 wt% FeO, but
preferably more like 5-7 wt% FeO). Scott Keuhner has offered me some of
his sanidines from the Leucite Hills, but they are zoned with respect to Fe
(I may try one of them anyway). I am familiar with the lists of feldspars
in DHZ and Smith and Brown, but use of many of those samples is problematic
because a) in many cases the Fe reported in the analysis actually came from
microinclusions in the feldspar, and b) many of those samples are now
unavailable.
So, I am seeking one Fe-rich plagioclase and one Fe-rich K-feldspar. I'd
need about 300 mg of pure sample for each, and both need to be free of
inclusions.
If anyone has access to such samples, or can put me on to a potential
source, I would GREATLY appreciate it.
Thanks very much!
-Darby
M. Darby Dyar
Dept. of Earth and Environment
Dept. of Astronomy
Mount Holyoke College
50 College St.
South Hadley, MA 01075
voice: 413-538-3073
fax: 413-538-2239
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C.V. GUIDOTTI Univ. Phone
(207) 581 2153
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