The distribution of the minor impurities, aluminium and silicon, between co-existing phases in altered ilmenite grains from three Western Australian localities has been investigated using SEM and electronmicroprobe analyses. A striking dependence of the impurity levels on the Ti/(Ti + Fe) fraction is observed. For compositions with Ti/(Ti + Fe) between 0.45 and 0.60, i.e. between ferrian-ilmenite and pseudorutile, the impurity content is virtually independent of Ti/(Ti + Fe), and is very low (0.2 wt. % Al2O3. 0.05 wt. % SiO2). For compositions between those of rutile and pseudorutile, there is a direct correlation between the impurity contents and the Ti content of the alteration phase. The impurity levels increase with increasing Ti/(Ti+Fe) to about 3 wt. % Al2O3 and 1 wt. % SiO2 for compositions close to TiO2. Thus during the latter stages of ilmenite alteration, alumina and silica are extracted from the ambient environment and are coprecipitated with, or adsorbed on to, the alteration products. The observed dependence of the alumina and silica contents on extent of alteration is consistent with a two-stage alteration mechanism earlier proposed (Grey and Reid, 1975).
ABSTRACT. A new magnesium aluminium phosphate mineral with the ideal formula MgsAIlz(PO4)a(OH)z 2 9 nil2 O (n -32) has been named aldermanite. It occurs as minute talc-like flakes, partly as an alteration product of fluellite, thinly coating cracks and cavities in a brecciated metamorphosed rock phosphate at Moculta, South Australia. Strongest X-ray diffraction lines are 13.40 A (100) 002, 7.98 /~ (80)
The Ka satellite or shake-off lines can be observed by wavelength-dispersive spectrometry on the highenergy side of the main Ka peak. Occasionally, chemical state analysis of an emitting atom has been attempted using the shape and position of these lines. Recent extensive theory and experiment have shown that it is fruitful to take a similar approach using extended x-ray emission fine structure (EXEFS) arising from the radiative Auger effect (RAE). This fine structure is found in a low-intensity spectrum on the low-energy side of the Ka peak.We have studied the RAE spectra of the Ka lines of the elements F through to Ca by EPMA. The RAE peaks have energies close to the KLL energies of Auger transitions. In the lighter elements in this series, it was found that the difference between Ka and the RAE peak energies becomes quite small. For elements lighter than fluorine, it is difficult to observe the RAE peaks because they are overlapped by the main Ka line. At the higher energy end of the series, the intensity of the RAE lines becomes very small. The utility of the RAE lines for state analysis is limited, in practice, to the elements F through to Ca. The extended x-ray emission fine structure (EXEFS) of the RAE spectra has been used to calculate local bonding parameters.Both shake-off and RAE spectra associated with the F Ka line have been studied experimentally in the rare earth fluorides. The KLL RAE moves to lower energy as the atomic number of the rare earth cation increases. This has been confirmed theoretically by calculating electron energies using discrete variational Xa molecular orbital theory. The shake-off peaks increase in intensity relative to the main Ka peak because atomic number increases, contrary to expectation. It is considered that this could be due to temporary covalency. The EXEFS of the RAE spectra has been used to calculate local bonding parameters.
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