Sergei and all,
The secondary fluorescence issue has been noted by many workers. The
only way that the F correction works is if there are no fluorescible
inclusions within 50-100 um. We use the F correction only to indicate when
there may be a problem with inclusions.
>Are there any refs where fluorescence of Cr is discussed? How good may ZAF
>account for the fluorescence?
>----- Original Message -----
>From: Eric Essene <[log in to unmask]>
>To: <[log in to unmask]>
>Sent: Wednesday, May 23, 2001 6:39 PM
>Subject: Re: TiO2 in Grt
>> We are very aware of the effect. We have documented the problem for
>> in even an iron-poor host (pyrope, olivine) with chromite inclusions, and
>> the effect can be shown to be important for 50-100 um at 15 kV (Cr is more
>> strongly fluoresced by Fe than Ti).
>> To Horst, Eric, and others
>> >Anyone studying the solubility of TiO2 in garnet grains
>> >containing small inclusions of a Ti-rich phase, such as
>> >rutile or ilmenit exsolutions, needs to be aware of the
>> >danger of spurious effects in electron microprobe analysis
>> >of the host garnet. Apparent titanium contents of up to
>> >1 weight-% TiO2 can result from secondary fluorescence
>> >effects, in the vicinity of such inclusions, and the effect
>> >is significant to a distance of 25-30 microns from the
>> >nearest inclusion. The problem has been documented for
>> >garnet by Feenstra & Engi (1998, notably in Fig.5 and
>> >text p.385-6).
>> >In essence, primary radiation generated by Fe and Mn in
>> >garnet causes the excitation of Ti-fluorescence radiation
>> >in nearby Ti-rich phases, even if no grain of the latter
>> >phase is hit by the electron beam. In samples that contain
>> >abundant such inclusions in garnet, it is virtually not
>> >possible to correct for this effect or indeed to avoid it.
>> >Ignoring this analytical artifact may produce unrealistically
>> >high Ti-contents for garnet (and other Fe-rich silicates).
>> >Best wishes,
>> >Martin Engi
>> >Feenstra A. & Engi M. (1998) An experimental study of Fe-Mn
>> >exchange between garnet and ilmenite. Contributions to
>> >Mineralogy and Petrology, vol. 131, p. 379-392.