The basic question how useful chemical analysis can be for quantitative
phase analysis of rocks is simply the ratio between the number of phases
and the number of main elements contained, i.e. the complexity of the
system. If you have rocks containing a big number of minerals maybe
having variable or unknown chemical formulae, and the number of unknowns
is bigger than the number of main elements, than the linear equation
system is under-determined and you can just calculate ranges of possible
mineralogical compositions. But of course in fortunate, simple cases it
is possible to calculate the mineralogical composition directly from the
XRF analysis.
In principle it is possible to add chemical constraints to a Rietveld
refinement. However, in my experience the qualitative mineralogical
analysis of rocks is a much bigger hurdle, and the typical uncertainties
in qualitative mineralogical analysis and the uncertainties of average
mineral formulae in complex rocks prohibit an effective use of this tool
for QPA.
Best regards
Reinhard
Am 14/02/2014 22:21, schrieb "Łukasz Kruszewski":
Hi. I think XRF can help only in case of simple samples or, e.g., to
disclude some "strange" elements, by proving there's none of them in the
particular sample. But when you have, lets say, a mixture containing a
spinel and periclase (MgO), then you won't be able to confirm by XRF
itself that all the Mg determined is cointained in periclase only, as
spinels take Mg too. An EDS or WDS system would be better here, but of
course it gives reasonable results for thin sections mostly. However, even
tiny 3D chunks of a sample can be used to confirm the presence of the
particular species you've included in the QPA refinement.
Good luck!
Luke Kruszewski
Hello all,
I use Rietveld primarily for quantitative phase analysis of rock samples.
We collect XRF and XRD data on our samples.
Is there a best practice for using these data together? Or a recognized
method or procedure for evaluating the agreement between the two? Can the
XRF be used to restrain the phase concentrations in a refinement?
Thank you all for the years of advice I have gotten from this forum.
All the best,
Blaise
--
TU Bergakademie Freiberg
Dr. R. Kleeberg
Mineralogisches Labor
Brennhausgasse 14
D-09596 Freiberg
Tel. ++49 (0) 3731-39-3244
Fax. ++49 (0) 3731-39-3129
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