Excess Free Energies of Mixing of Sr,Ba-Bearing Binary Feldspar Solid Solutions (Experimental Data)

A. R. Kotelnikov and I. V. Chernysheva
Institute of Experimental Mineralogy Chernogolovka, Moscow distr., 142432, Russia
Vernadsky Institute of Geochemistry and Analytical Chemistry, Kosygin str., 19, 117975, Moscow, Russia

Abstract: The distribution of potassium and strontium, potassium and barium between feldspars and aqueous chloride solutions was studied at 700°C, 2 kbar and 800°C, 2 kbar respectively. The distribution of Sr and Ba between coexisting feldspar and chloride solutions is not ideal; Sr and Ba are enriched in feldspar relative to solution. In order to estimate the phase state of the chloride solutions, special experiments were conducted using the synthetic fluid-inclusion method in the systems KCl-BaCl2-H2O and KCl-SrCl2-H2O at 700–800°C, 2 kbar. It was shown that (0.5M KCl+0.5M SrCl2) aqueous solution is homogeneous at 800°C, 2 kbar. The 0.25–0.5M SrCl2 solutions are homogeneous at 700°C 2, kbar. The (0.5M KCl+0.5M BaCl2) solution is homogeneous at 700°C, 2 kbar and heterogeneous at 800°C, 2 kbar. Margules parameters for describing the excess energy of mixing of the (K,Sr)- and (K,Ba)-feldspar solid solutions were calculated. The integrated values of excess energy of mixing (Gintex) were estimated for the different binary feldspar solid solutions, and a correlation of Gintex with the crystallochemical parameter ρ = (RA-RB)/D(Me-O) was observed. Feldspar solid solutions can be subdivided into three groups based on the relationship between Gintex, p and the stability of the solid solution.

Keywords: (K,Sr) and (K,Ba) feldspar solid solutions • ion exchange equilibria • mixing properties

Mineralogical Magazine; March 1995 v. 59; no. 394; p. 79-91; DOI: 10.1180/minmag.1995.59.394.07
© 1995, The Mineralogical Society
Mineralogical Society (www.minersoc.org)