Epitaxy in the Crystallization of Feldspar Gels and Glasses

The crystallization behavior of stoichiometric feldspar gels and glasses before and after seeding has been compared, and the role of epitaxy in their crystallization upon seeding has been studied. The crystallization products were mainly determined by X-ray diffraction (XRD) analysis and epitaxy upon seeding was examined with a scanning electron microscope (SEM), and energy dispersive spectrometry (EDS). It was found that upon isostructural seeding, Na and K-feldspars crystallized epitaxially from their gels and/or glasses. Little or no seeding effect was found in CaAl{sub 2}Si{sub 2}O{sub 8} and SrAl{sub 2}Si{sub 2}O{sub 8} gels and glasses. Isostructural seeding in BaAl{sub 2}Si{sub 2}O{sub 8} gets increased the formation of Ba-feldspar (monoclinic celsian) epitaxially, whereas without seeding hexacelsian was the crystallization product.