Abstract

The crystal structure of albite from Tiburon, Marin County, California, has been refined from three-dimensional X-ray intensity data collected on an automatic single-crystal diffractometer at 500, 750, and 970°C (all ±10°C) to R factors of 0.032, 0.035, and 0.039 for 1980, 1990, and 2002 reflections respectively. The vibrational amplitude of the sodium atom exhibits a linear dependence on temperature and extrapolates to zero at 0 К within error limits, implying that the high anisotropy of the electron-density distribution about the Na position is strictly a result of anisotropic thermal motion. Structural adjustments to thermally induced stresses are principally associated with T-O-T angles as opposed to distortion within the aluminosilicate tetrahedra. Whereas Na-O bond lengths increase substantially with increasing temperature, the T-O bond lengths show little change. The apparent slight shortening of the T-O bonds is attributed to errors in bond-length calculation caused by thermal motion.

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