Complete analysis of hydrous minerals by inductively coupled plasma emission spectroscopy and electron probe X-ray microanalysis

Abstract

Complete analyses of hydrous minerals, muscovite and several zeolites, by inductively coupled plasma optical emission spectroscopy (ICP-OES) involving silicon and by electron probe X-ray microanalysis (EPMA) involving oxgen were carried and the results were compared with each other. For the ICP analysis, (1020) mg mineral sample was decomposed with a mixture of hydrochloric and hydrofluoric acid in a Teflon vessel, and after the addition of boric acid to mask excessive fluorine, emission intensities of the elements were recorded. Contents of water were determined by the ignition loss (muscovite) as well as thermo-gravimetric analysis (zeolite). In the EPMA analysis, the ZAF correction was employed, in which Dumcumb-Reed's atomic number correction, Casting-Reed's fluorescence correction, and authors' absorption correction were applied.
f(x)=A{exp(u² )Erfc (u)-B exp (v²) Erfc(v)}
Empirical formulas of muscovite from Fukushima pref. obtained by ICP and EPMA analyses are as follows :
ICP (K_0.84Na_0.10Ca_0.01)∑_0.95(Al_1.73Fe_0.19Mg_0.01)_∑1.93- (Al_0.80Si_3.20)_∑4O_9.85(OH)_2.16
EPMA (K_0.96Na_0.10)_∑1.06(Al_1.73Fe_0.20)_∑1.93(Al_1.04 Si_2.96)_∑4O_9.79(OH)_2.22
Formulas obtained by the two methods are in good. agreement with each other. The value for water content of 4.9 % given by ignition loss was agreement with that of 4.95 % given by EPMA. Small differences in the empirical formulas of several zeolites may be due to the reason that in the ICP analysis, the determined content of water is the average of the sample, while in the EPMA analysis, the value represents that of the micro area bombarded by electron.