Reinvestigation of the structure of low cristobalite

Abstract

Twinned crystals of low cristobalite from Ellora, Hyderabad, India were found to have space group P 4 1 2 1 (or P 4 3 2 1 ) and cell dimensions a = 4.978 and c = 6.94 8 Å. A three-dimensional full-matrix least-squares refinement based upon 110 integrated intensities which were corrected for the effects of twinning, confirmed Nieuwenkamp 's original structure and reduced the final R value to 4.4%. The refined set of four positional parameters are; u =.30004 ±.00033, x =.23976 ±.00089, y =.10324 ±.00085, z =.17844 ±.00052. These refined parameters lead to Si–O distances of 1.601 ±.004 and 1.608 ±.004 Å.