NASA TN D-6980 APPLICATION OF THERMODYNAMICS TO SILICATE CRYSTALLINE SOLUTIONS
i FOREWORD iii ACKNOWLEDGMENTS v SYMBOLS ix 1 THERMODYNAMIC RELATIONS IN CRYSTALLINE SOLUTIONS 1 2 THERMODYNAMIC STABILITY OF A SOLUTION 11 3 COMPOSITION OF COEXISTING PHASES 15 4 MEASUREMENT OF COMPONENT ACTIVITIES BY ANALYSIS OF PHASE DIAGRAMS 25 5 MEASUREMENT OF COMPONENT ACTIVITY USING COMPOSITION OF COEXISTING MINERALS 35 6 ORDER-DISORDER IN Fe-Mg SILICATES 39
A mineral chemical study of a metamorphosed iron formation in northern Sweden
The composition of coexisting biotite, Ca-amphiboles, and iron oxides in a metamorphic iron formation in Northern Sweden, analysed by micro-probe technique, is correlated with the oxygen pressure as indicated by the presence of distinct iron oxide minerals. A close approach to chemical equilibrium during metamorphism is indicated by regular element distribution between the phases and the restriction of the Mg/Fe ratio and Ti/Mg+Fe+Ti ratio of the ferromagnesian silicates in presence of magnetite and hematite. The use of iron-titanium oxides as indicators of oxygen pressure in rocks is discussed. There is an increase of the Mg/Mg+Fe 2+ and the ferric-ferrous ratios, and a decrease of the Ti content in the silicates with increasing oxygen pressure. Different ways in which biotite and Ca-amphiboles stabilize at increasing oxygen pressure are investigated. The role of water in the rocks during metamorphism is discussed.
The statistics of superexchange interaction and ionic distribution in substituted ferrimagnetic rare earth iron garnets
Abstract Ideas on the statistics of superexchange interaction developed and applied to substituted yttrium-iron garnets by Gilleo are extended and applied to substituted rare earth iron garnets. It is shown by means of structural considerations that only four interactions per c site ion with d site ions are important in determining the contribution of the c site ions to the 0°K saturation magnetization. The statistical theory accounts especially well for the behavior of n B (0°K) vs. x (= y + z ) of the system {Gd 3 }[Al y Fe 2− y ](Al z Fe 3− z )O 12 and for {Gd 2.4 Ca 0.6 }[Al y Fe 2− y ](Al z −0.6 Si 0.6 Fe 3− z )O 12 corrects the previously obtained ionic distribution which had been considered anomalous. Other systems are also considered. Crystal chemical aspects of some of the results, compensation points and some minor limitations of the treatment are discussed.