THE SYSTEM DIOPSIDE-ANORTHITE-AKERMANITE A DISSERTATION Presented in Partial Fulfillment of the Requirements for the Dep-ree Doctor of Philosophy in the Graduate School of the Ohio State University ' '' E. Christiaan de Wys, A.B., M.A. The Ohio State Universitv 1955 Approved by: 0 Advisor department of Kineralopy A c knowled gment s .Vith deep gratitude the writer acknowledges his indebtedness to Dr. W.R. Foster, without whose constant encouragement, and friendly guidance completion of this investigation would not have been possible. The writer also wishes to express his appreciation to the faculty of the Department of Mineralogy of Ohio State University, for the research facilities afforded and training received. The author especially wishes to extend his thanks to his wife, J.B.N. de Wys, for her patience, constant assistance, and typinr of the dissertation. Thanks are due also to H.H. Uotila for the final preparation of the diagrams. Table of Contents page Acknowledgements ii List of Tables iv List of Illustrations v Introduction 1 Some Occurences of the Minerals 5 Characteristics of the Minerals 11 Experimental Procedure 20 Thermal Data 24 Thermodynamic Analysis of the System Anorthite-Akermanite 39 Discussion and Conclusions 45 Bibliography 49 Autobiography 57 iii List of Tables Table No. paye 1 Optical data of CaAl2Si20g 12 2 Melting point of anorthite 14 3 Heat of fusion of anorthite 15 4 Meltinp point of diopside 16 5 Melting point of akermanite 18 6 Heat of fusion of akermanite 18 7 Thermal data for the system anorthite-akermanite 31 8 Thermal data for the system diopside-anorthite-akermanite 36 List of Illustrations Figures page 1 The lime-magnesia-silica tetrahedron 4 2 Index of refraction chart for glasses of the system anorthite-akermanite 22 3 Index of refraction chart for glasses of the system diopside-anorthite-akermanite 23 4 Equilibrium diagram of the system diopside-anorthite 26 5 Equilibrium diagram for the system diopside-akermanite 27 6 Equlibrium diagram for the system anorthite-akermanite 28 7 Equilibrium diagram for the system diopside-anorthite- akermanite 33 8 Equlibrium diagram for the system diopside-anorthite- akermanite on the basis of the data of Osborn et al. (1954) and Prince (1954) 35 9 Comparison of theoretical and experimental liquidus curves for the system anorthite-akermanite 40 v Introduction This study presents the results of an investigation of the high temperature phase equilibrium relationships in the binary system anorthite (CaAl2 Si2 0 g) - akermanite (Ca2 MgSi2 0 y) and in the ternary system diopside (CaMgSigO^) - anorthite (CaAl2 Si2 0 g) - akermanite (Ca2MpSi20y). The well known quenching technique was employed. The two sjrstems lie within the quaternary system CaO-MgO-A^O-j-SiC^. The interior of this four component system is made up of numerous sub­ systems, at least some of which are true binary, ternary and quaternary systems. The present work deals with that portion of the large quaternary system in which the composition can be expressed in terms of the component-'- Ca0 .MgO.2 Si0 2 , CaO.A^O^. 2 Si0 2 , and 2Ca0.Mg0.25i02« Such ternary planes serve to partition the interior of the tetrahedron into smaller tetrahedra which can be isolated and investi­ gated individually. If the plane diopside-anorthite-akermanite proves to be ternary it will serve as a partition separating liquids which, during crystallization, must remain on one side of this partition from those which must remain on the other side. This is true whether frac­ tional or equilibrium crystallization takes place. An illustration of the general quaternary system CaO-KgO-AlgO^-SiC^ is presented in Figure 1. This figure indicates the position of the diopside-anorthite- akermanite plane in the tetrahedron. A hollow, transparent tetrahedron has been used to permit a clearer view of the plane under consideration. 1. Ca0.MgO.2SiC>2, CaO.A^O^.2Si02 and 2Ca0.Mg0.2Si02 are, of course, merely the oxide formula equivalents of CaMgSi^O^, CaA^SigOg, and Ca2 NpSi0 y respectively. 1 2 The system CaO-MgO-SiOg-A^O-j has considerable petrologic and industrial improtance. The three silicates investigated in this research were chosen since they occur in basic igneous rocks, metamorphic hybrid zones, and in industrial slags. Anorthite and diopside are well known in rocks of common petrologic interest, while all three of the silicates are important in the composition of slags. One of the purposes of experimental research of this nature has always been to clarify the relationships of mineral associations, of magmatic or metamorphic origin, observed by the petrographer. With the exception of the iron and alkali content the basic magmas may be reason­ ably well expressed in terms of the components GaO, MgO, A^O-^, and SiC^. In metamorphism the phase assemblages of some of the calcareous-aluminous metamorphosed rocks fall within this quaternary system. Technologically, some of the industrial glasses, cements, and virtually all usual iron blast furnace slaps are included in the lime- magnesia-alumina-silica system, according to McCaffery et a l . (1927), Koch (1933), Osborn et al. (1954), and Prince (l95l)« Since apparently the properties of slag are not mere composites of the properties of Si02, A^O-^, MgO, and CaO, but rather of the mineral compounds present (McCaffery et al.), an investigation of the interrelationships of some of the minerals should be useful. According to Martin and Derpe (1943) a knowledge of possible structural units in the slaps would clarify greatly the nature of chemical reactions in such fluid, and would help to explain reactions between the slag and metal. Such knowledge would facilitate a greater control of slag chemistry. Accordingly, a thermo­ dynamic analysis of the system anorthite-akermanite was undertaken in 3 an attempt to formulate possible structural units present in the liquid phase, A number of investigators (McCaffery et al,, 1927), (Janecke, 1933), (Nurse and Midgley, 1951), (Osborn et al,, 1954), (Prince, 1954) have indicated that anorthite, pyroxene, and melilite form a stable equilibrium phase assemblage. But no detailed investigation of the liquidus relations for the diopside-anorthite-akermanite system has ever been carried out. There has been no clear indication as to whether anorthite can coexist with pure akermanite. Since the stability of akermanite below a certain temperature has been seriously questioned (Carstens and Kristofferson, 1931), (Bowen et al,, 1933), (Osborn and Schairer, 1941), (Neuvonen, 1952), it appeared desirable to consider this matter in some detail. u A I2 ° J 0 Mu 9 Si Co lSIO. Ak Fo Mor Mo CaO MgO Kir. 1 The lime-marnesia-alumina-silica tetrahedron. The shaded area represents the anorthite-akermanite-diopside ternary plane. The abbreviations have the following simi- ficance: An - anorthite; D - diopside; Ak - akermanite; Mu - mullite; Si - sillimanite; Sp - spinel: Co - cordierite; n - <-ehlenite; L - lamite; R - rarkinite; W - vrollastonite; Mer - merwinite; Mo - monticellite; Fo - forsterite; Cl - elinoenstatite. Some Occurences of the Minerals Anorthite This mineral belongs to the important feldspar group which constitutes about 59*5$ of all the igneous rocks (Burgess, 1949)* It is the lime rich member of the plagioclase, or soda lime, feldspars and is relatively rare compared with the other members of the series. Impure anorthite is present as an essentiall constituent in such basic igneous rocks as andesite, basalt, diorite, gabbro, and norite (Barth, 1936). Good crystals of anorthite occur at Mount Somma, in Italy, where they occur as glassy crystals in the old lavas in association with spinel and leucite. In India anorthite is found as a gangue of corundum. It is also observed in the druses of ejected volcanic blocks, as well as in the granular limestones of contact deposits, near Trenlino, Italy. In Japan it is found in the lavas of the island of Miyake. Some anorthite is found in meteorites (Grout, 1932). Anorthite also occurs in metamorphic assemblages. Turner (1933) states that anorthite is an antistress mineral. Anorthite is apparently typically found in the amphibolite facies (Turner, 1948), a critical mineral assemblage formed during progressive metamorphism of basic igneous rocks. It is then associated with hornblende. .Viseman (1934) found anorthite associated with the red ^arnets in the epidorites of the Scottish highlands. Grubenmann and Niggli (1924) found anorthite in the kata-metamorphic zone where it is associated with garnets, vesuvianite, calcite, periclase, diopside, hornblende and others. Anorthite is also present in a variety of technicological products. In basic slags it is an important constituent (McCaffery et al. (1927), (Koch, 1933). It is sometimes found as scum on stone-ware bodies made of white firing clay (Knizek and Fetter, 1945). Rigby and Green, (1942) observed the formation of anorthite in fireclay or fireclay prop containing additions of dolomite or asbestos. Hugill and Green (1939) drew attention to the ease with which anorthite forms whenever fireclay materials are attacked either hy pure lime or by lime-bearing slaps. St. Pierre (1955) noted the formation of anorthite during the firing of bone-china bodies. De Ville (1955) found that anorthite develops in talc whiteware bodies when wollastonite is substituted in whole or in part for talc. Diopside Dionside is a member of the important pyroxene group of minerals. Of the two main reaction series encountered in the basaltic lavas, the pyroxene series constitutes one and plarioclase the other (Bowen). Consideration of these two series goes far towards explaining the essential features of the crystallization process in the basaltic lavas. Barth (1936) concludes that most natural basalts lie on the boundary curve separating the primary fields of pyroxene and plagio­ clase. Some diopside is found in the granite family as phenocrysts in the aphanites (Grout, 1932). Diopside occurs in the alnoitic rocks at Isle Cadieux in Canada (Bowen, 1922). There it is associated with biotite, olivine, melilite, and oerovskite.