What question did this study set out to answer?

To investigate the cation exchange reaction between RbAlSi3O8 and BaCl2 under hydrothermal conditions.

March 26, 2026Geochemistry International0 citations

Experimental Study of RbAlSi3O8–BaAl2Si2O8 Solid Solutions: Cation-Exchange Equilibria with Fluid

AKA. R. Kotelnikov NSN. I. Suk ZKZ. A. Kotelnikova

Key Points

To investigate the cation exchange reaction between RbAlSi3O8 and BaCl2 under hydrothermal conditions.
Conducted the cation exchange reaction at 650°C and 2 kbar.
Refined unit-cell parameters of (Rb,Ba)-feldspar solid solutions.
Applied the two-parameter Margules model to describe excess mixing volume.
Ba preferentially partitions into (Rb,Ba)-feldspar relative to fluid across all compositions.
Negative excess mixing volume described by WV1 = –2.11 ± 0.05 cm3/mol and WV2 = –1.85 ± 0.06 cm3/mol.
Calculated excess mixing energy: WG1 = 6.82 ± 0.54 kJ/mol and WG2 = 12.25 ± 0.81 kJ/mol.

Abstract

The cation exchange reaction 2RbAlSi3O8 + BaCl2(aq) = BaAl2Si2O8 + 4SiO2 + 2RbCl(aq) was studied under hydrothermal conditions (T = 650°C and P = 2 kbar). It was shown that Ba partitions preferentially into (Rb,Ba)-feldspar relative to fluid over the entire compositional range. The unit-cell parameters of (Rb,Ba)-feldspar solid solutions were refined. The excess mixing volume is negative and can be described by the two-parameter Margules model: WV1 = –2.11 ± 0.05 and WV2 = –1.85 ± 0.06 cm3/mol. Based on the distribution of Rb and Ba between feldspar and fluid, the excess mixing energy of the solid solution was estimated: WG1 = 6.82 ± 0.54 and WG2 = 12.25 ± 0.81 kJ/mol. The calculated excess mixing functions were compared with those of other feldspar solid solutions.

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