Entropy Estimates for Some Silicates at 298°K from Molar Volumes

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Science  24 Sep 1976:
Vol. 193, Issue 4259, pp. 1241-1242
DOI: 10.1126/science.193.4259.1241


Third law entropies for silicates of Be, Mg, Ca, Zn, Na, and K containing the same anion group, for example, SiO4 or SiO3 or AlSi3O8, are found to be linearly related to their molar volumes. The relationship between the molar volume and the entropy of silicates of Fe and Mn, atoms with unfilled d electron subshells, is different from that of other silicates. The linear correlations yield a useful method of estimating the entropies of ortho-, meta-, and framework silicates (feldspars and feld-spathoids). The estimated entropies of pyrope and almandine at 298°K are 47.47 and 68.13 gibbs per mole, respectively.