Experimental Studies on Micas: A Synthesis

Abstract
The principal end ineinbers of the micas believed to be common in sediments have been synthesized and some of their stability relations determined. The polymorphs of musco- vite and paragonite, the principal dioctahedral end members, obtained were 12r 1 M and 2MI, and those of phlogopito and annito, the principal trioctahedral end members, 1Md and llV( or 3T. The range of stability of each of the polymorphs could not be fixed accurately because of the siow rate of transformation ; however, the transformations 1Md-~ IM-~ 2N( I were effeeted for muscovite and paragonite and IM--~ livid or 3T and 2M I --> li3/i or 3T for phlogopite. The growlh characteristics of these micas in the laboratory are believed to be analogous to the formation of micas in sediments. Knowledge of the synthetic micas contributes greatly to an understanding of the natural materials called illite, hydromica, and high-silica serieite. The dioetahedral members of these materials and related minerals may be delineated accurately in the system museovite--Al-eeladonite--pyrophyllite and their iron analogues. The triocta- hedraI members of some of the same materials may be outlined in the system phlogopite-- eastonite--tale and their iron anMogues. The postulated substitution schemes in these systems are mainly MgSi ~ AIVIAIIV, KA1 ~- Si, and HsO ~ K. In materiMs inter- mediate between these systems, such as most biotites and vermiculites, the substitution of 31Vfg _~ 2AlVI is of major importance. The mixed-layer structures involving micas are elucidated.

This publication has 3 references indexed in Scilit: