Abstract
The influence of additions of CaO, SrO, BaO or Li 2O to a synthetic albite feldspar glass was investigated by 29Si, 27Al and 23Na MASNMR spectroscopy. All oxides induce more ordering of the “SiO 4”, “AlO 4” tetrahedra in the glass when present in greater (CaO > 60 mol % relative to SiO 2) or lesser (Li 2O > 30 mol %) proportions. Larger additions of CaO (80, 100 mol %) induced crystallization of calcium silicate phases but similar additions of SrO or BaO stabilized the glass phase. 27Al MASNMR data suggested that large additions of CaO caused the separation of an aluminate phase; the data also revealed the presence of octahedral Al 3+ sites for all additions of MO (M = Ca, Sr, Ba), however, no octahedral aluminium was seen in the presence of LiO 2. The apparent 23Na chemical shift generally moved to lower field as the proportion of “AlO 4” in the glass increased.
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