Illustrative Example: Analysis of a Feldspar Mineral
Figures 1-6 below show the XPS high resolution spectra of the elements on the surface of a freshly ground Feldspar sample. High resolution analyses are used to determine the various chemical species in the sample. Three component peaks were found in each spectrum corresponding to three different phases as listed below. There are many varieties of feldspar, but those commonly identified are Soda Feldspar (Na2O • Al2O3 • 6 SiO2), Potash Feldspar (K2O • Al2O3 • 6 SiO2), and the Calcium Fledspar (CaO • Al2O3 • 2 SiO2). The Feldspar in the present case is a rather complex compound and has three different chemical phases with Phase 1 as the major phase followed by the minor Phases 2 and 3. We have taken advantage of the differential charging of each of these species to identify each as a separate species. The same material without differential charging would appear to have the weighted average of these three compositions.
Phase 1: Na2O • 0.76 K2O • 1.59 Al2O3 • 12.64 SiO2 • 0.84 H2O
Phase 2: Na2O • 0.33 K2O • 1.26 Al2O3 • 7.86 SiO2 • 8.48 H2O
Phase 3: Na2O • 0.19 K2O • 1.62 Al2O3 • 7.25 SiO2 • 9.79 H2O
This feldspar is really a composite material made of three different oxides, each with its own degree of hydration. The main phase has a relatively low degree of hydration, but the two minor phases are highly hydrated. In some applications the presence of the two highly hydrated chemical phases is important.