MINERAL CHEMISTRY OF SOME SYNTHETIC CANCHINITES

Abstract

A survey of the literature shows that the Cancrinites have a complex chemistry and a confusing nomenclature. The approximate composition of these minerals Can be expressed as 3NaAlSio4.R(CO3,SO4,Cl,OH) nH2O, where R = Na,Ca,K. Using the terminology and approximate compositions proposed by Winchell and Winchell (1951). for the various end-members of this mineral, the fields of synthesis and cell parameters of eight different cancrinites have been determined in the temperature range 200° to SOOoC. and at water pressures of 10,000 to 30,000 psi. Some of the compositions proposed by Winchell and Winchell (1951) failed to synthesize cancrinites, but instead synthesized sodalite type minerals. As a result the nomenClature of the cancrinites has been revised. A consideration of the temperature limits of syntheses of cancrinites possibly indicates that the controlling factor in their fields of syntheses is the cation attached to the carbonate, hydroxide, sulphate and chloride radicals, rather than the anionic radicals themselves. A similar type of control seems to effect the size of the unit cell volumes of these minerals. At low temperatures analcite appears as a second phase in many of the cancrinite compositions. Several possible explanations of this low temperature analcite are discussed. The sodium carbonate and bicarbonate cancrinites Undergo a polymorphic transition to a hauyne-nosean type of mineral. A similar polymorphism exist in sodium hydroxide cancrinites. The experimentally determined curves possibly represent metastable equilibrium. A discussion of the general conditions of equilibrium, the identification of the synthetic products and their applications to the cancrinites is given. Preliminary investigation of the extent of solid solution between some end-members of the cancrinites indicates that complete solid solution between these end-members may not exist. Results of cell parameter determinations of some of the synthetic cancrinites show good agreement with four natural canorinites investigated in this thesis.