Structural inheritance in the formation of mica from kaolin minerals under hydrothermal conditions

Abstract

View related articles S t r u c t u r a l i n h e r i t a n c e in t h e formation of mica from kaolin minerals u n d e r hydrothermal conditions N.V. Kotov et 01.The problem of structural inheritance i n hydrothermal transformations of kaolin minerals into mica has been discussed in several special studies (Frank-Kamenetskiy et al., 1970; Vyakhirev e t al., 1974;Frank-Kamenetskiy and Kotov, 1975; Goylo, 1975). In particular, it has been established that muscovite and paragonite of types 1M + 2bI1 and II respectively are formed from 1Tc kaolinite in media containing potassium and sodium chlorides and hydroxides; that a mixture of mica polytypes, with 2M1 predominating over l M , is formed from dickite (2M1 modification) ; and that structurally disordered micas are formed from disordered halloysite. , It has also been shown in experiments using short reaction times that mica synthesis precedes the formation of composite-sheet mica-montmorillonite forms, because these structures are formed in a stage-by-stage process (FrankKamenetzky et al., 1971;Frank-Kamenetskiy et al., 1974). A. N. Tomashenko (1978) has noted that new sheet forms can be synthesized in this process in the following ways: 1) by a structural transformation mechanism with disruption and building out of alternate layers, so that the sequences of layers carry information on the polytype, and with partial removal into the vapor phase of A1 and Si which a r e not participating in the topotactic restructuring proper (see also the earlier papers by Goylo, 1975, andKotov, 1975); 2) with the introduction of Si or Al, if the nature of the reactants allows, necessarily resulting i n building out of the 1:l structure into a 2:l structure, a process that brings about complete polytype inheritance; 3) through solution of the initial forms and crystallization of new forms from solution. The pH of the medium has a major effect on the course of such reactions. Translatcd from Strukturnaya preycmstvcnnost' pri slyudoobrazovanii PO kaollnovym mincralarn v gidrofermal'nykh usloviyakh, AN SSSR Izvcstiya, scr. geol., 1980, no. 12, p. 68-80. Co-authors with Kotov are S. V. Soboleva, E. A. Goylo. D.B. Zvyagin and V.A. Frank-Kamenctskiy. They arc with Leningrad University, Leningrad, and the Institute of Geology of Ore Dcposits, Petrography, 3lineralogy. and Geochemistry (IGELI), of the USSR Academy of Sciences, AIoscow.

Structural transformations of kaolins into (Ni, Al) serpentine-like phases and subsequently into trioctahedral micas under hydrothermal conditions

“…The first alternative need not affect the orientation of octahedra and might lead to the formation of micas with different polytypic structures, depending on whether the starting material was a kaolinite (1M) or a nacrite (2M2). While this mechanism has been successful in dioctahedral micas (Frank-Kamenetskii et al, 1978;Kotov et aL, 1980), it apparently did not prevail in the present experiments, even if the additional Si,Al-containing phases were available as a source of elements needed to form the tetrahedral sheet.…”