Stepwise multiple regression analyses of the apparent R(SiO) bond lengths were completed for coesite and for the silica polymorphs together with the clathrasils as a function of the variables fs(O), P (pressure), fs(Si), B(O), and B(Si). The analysis of 94 bond-length data recorded for coesite at a variety of pressures and temperatures indicates that all five of these variables make a significant contribution to the regression sum of squares with an R2 value of 0.84. A similar analysis of 245 R(SiO) data recorded for silica polymorphs and clathrasils indicate that only three of the variables (B(O), fs(O), and P) make a significant contribution to the regression with an R2 value of 0.90. The distribution of B(O) shows a wide range of values from 0.25 to 10.0 Å2 with nearly 80% of the observations clustered between 0.25 and 3.0 Å2 and the remaining values spread uniformly between 4.5 and 10.0 Å2. A regression analysis carried out for these two populations separately indicates, for the data set with B(O) values less than three, that fs(O) B(O), P, and fs(Si) are all significant with an R2 value of 0.62. A similar analysis for the remaining data indicates that only B(O) is significant with an R2 value of 0.52. The relationships between these results and those published previously are discussed.

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