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
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).
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.