Date: Mon, 19 Sep 1994 10:29:31 -0500
Subject: Re: biotite analysis problem
From: klivi@JHUVMS.HCF.JHU.EDU
Message-Id: <01HHAK9931EQQQRTWV@JHUVMS.HCF.JHU.EDU>
Mime-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-Transfer-Encoding: 7BIT

John,
Just got back from the IMA conference in Pisa, Italy.
We had a problem with sheet silicates when we used the ZAF routine
supplied with the TN-5500 (TASK) - the sums were too low. When we started
using CITZAF from Cal. Tech. our problems went away. Do you normally have
problems with sheet silicates? I'm surprized that garnet analyses are
normal (i.e., total 100%). We still can't get a garnet analysis to come
down consistently to 100% without using a garnet standard for Si and Al. I
guess you are using the the muscovite for Si and Al and F-phlog for Mg and
F. I would tend to stay away from sheet silicates as standards, except for
F in F-phlog. If you remember, we use feldspars, pyroxenes, and olivines
for most of our standards. Try using different standards (e.g., Si and Al
on anorthite, Fe and Mg on pyroxenes). How is the stoichiometry of the
biotite? There is not much to go on with a biotite but maybe you can
identify a screwy element (but probably not).
If in the end, only these biotites give you problems, it is
probably due to some missing element (there is also the possibility of NH4
and Cl).
Good luck and let me know if I can help any more.
Ken