Scientia Sinica

PRELIMINARY RESULTS ON THE HYDROTHERMAL SYNTHESIS OF BRITTLE MICAS*

Tu Kwane-Cum (#36)

(Institute of Geology, Academia Sinica)

INTRODUCTION

There have been controversies among geologists as to the role played by the shearing stress in mineral formation. Micas, chlorites and brittle micas are listed by Harker!! as stress minerals, whose stability field on the temperature-pressure diagram is extended bythe introduction of stress. Larsen!) expresses doubts as to the importance attributed to stress by Harker, while Read states that “all stress minerals can be formed under no stress condition.”

In the past two decades, it has been shown experimentally that various members of the mica group can be made under high vapour pressure in the absence of stress! 8% 10.16 1718, 21,22] Tyo synthesis of Mg-chlorite in bombs free from stress was also reported!*!. Tt remains to be proved whether brittle micas could be prepared without applying any differential stress, and if they could be synthesized at all to investigate their stability range with respect to temperature, pressure, and concentration. With this view in mind, the author conducted a series of experiments in the attempt to prepare brittle micas under hydrostatic pressure. The results of experiments and their geologic interpretations are given below. It is necessary to point out that no brittle micas

have ever been successfully synthesized, though a doubtful artificial margarite "was reported to have been observed by Chroustchoff™! in his work on mica synthesis.

MetHops oF INVESTIGATION

About 30 experiments were performed, in which a stainless steel bomb was used, similar to that described by Morey and Ingerson!!, The temper-

*To be published in Chinese in Acta Geologica Sinica, Vol. XXXVI, No. 2, 1956.

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