Molar volumes on the clinochlore-amesite binary: some new data

Unit-cell parameters for Mg-chlorites on the clinochlore (clin)-amesite (ames) binary, within the composition range (Mg 5 Al)(Si 3 Al)O 10 (OH) 8 -(Mg 4.6 Al 1.4 )(Si 2.6 Al 1.4 )O 10 (OH) 8 , are presented. The compositional dependences are: a (A) = 5.3425(6) − 0.0180(5) X, b (A) = 9.2603(43) − 0.0340(36) X, c (A) = 14.604(30) − 0.198(24) X, and β( 0 ) = 96.966(58) + 0.127(48) X, where X is the extent of Tschermak substitution, defined by Mg 6 Si 4 O 10 (OH) 8 + X Mg −1 Si −1 Al 2 . Molar volume data, fitted to an ideal solution model, can be expressed as V (cm 3 mol −1 ) = 215.93 (± 0.57) − 4.46 (± 0.47) X, giving V clin 0 211.47 ± 0.12 cm 3 mol −1 and V ames 0 = 207.01 ± 0.38 cm 3 mol −1 . A regular symmetric model gives V clin 0 = 211.58 ± 0.10 cm 3 mol −1 , V ames 0 = 210.30 ± 1.66 cm 3 mol −1 , and W v = − 5.39 ± 2.68 cm 3 mol −1