Solubility of KFe3+Si2O6 in Leucite

Published chemical analyses of leucites (Deer et al. 1963) show that their departure from stoichiometric composition is not very significant. Most studies on leucite ss are related to the substitution of potassium by sodium, which was considered to be very limited by Bowen and Ellestad (1937). Experimental studies by Fudali (1963) established that such a substitution is more extensive in the system KAlSi2O6-NaAlSi2O6. Incorporation of the compound K2MgSi5O12 by leucite has been studied by Schairer (1948), who established a complete series of solid solution through the substitution of MgSi ⇌ AlAl between K2Al2Si4O12 and K2MgSi5O12. However, no experimental data are available on the extent of solubility of iron in leucite. The reported chemical analyses of leucite (Faust 1963; Deer et al. 1963) show a prevalence of Fe3+ over Fe2+, which can be related to substitution of Al3+ by Fe3+ in the tetrahedral sites. Leucites from potassic lavas of the Leucite Hills contain more than 2% Fe2O3 (Carmichael 1967) and there is a relative excess of Si and K over Al. Leucites from other areas show much lower contents of iron (Faust 1963) in spite of the similar bulk compositions of the host rocks. Stability of the KFeSi2O6 (FeLc) compound and its crystal structure was studied by Faust (1963). The extent of solid solution of KFe3+Si2O6 in leucite at 1 atm and at pressures of 1 and 2 kb will be discussed in the following pages. The study was made under partial pressure of H2O2 in order to ensure highly oxidizing conditions.