Scientia Sinica

No, | TU; PRELIMINARY RESULTS ON HYDROTHERMAL SYNTHESIS OF BRITTLE MICAS 183

addition, they are very rare in nature. The meager occurrencés of margarite high in Na manifest that they formed under unusual conditions.

With the introduction of Mg salts into the initial charge, aluminous serpentine was yielded, instead of clintonite, as would have been desired (Expt. 13). This indicates that Ca ions stayed in solution and did not participate in the crystal structure of serpentine.

Our experimental findings are in accord with the geological facts in that serpentine is far more widespread than the Mg-Ca brittle micas. In nature the formation of serpentine is frequently accomnanied by carbonatization, indicating that the Ca ions likewise stayed out of the serpentine structure. Apparently, the chemical reaction in nature tends to favour the formation of serpentine, talc, carbonate (the so-called process of listwanitization) rather than the Mg-Ca brittle mica, when the reaction involves the same chemical elements in similar proportions.

There is reason to suspect that the presence of Fe might conceivably widen the stability range of brittle micas, especially toward the low temperature side. According to Betechtin”!, chloritiod forms in the earlier stages of regional metamorphism; in more intensively metamorphosed rocks chloritoid is not observed. This means that a low temperature condition would probably favour the formation of the Fe brittle mica. The author noticed a similar situation in his work on the synthesis of chlorite?3).

In conclusion, it should be noted that the fact that members of the brittle mica group occur mainly in metamorphic rocks likewise indicates that the presence of stress might extend their stability field. Further research work is to be done before this can be proved.

REFERENCES

{ 1] Barth, T. F. W., 1932. The Structures of the Minerals of the Sodalite Family. Zeits, Krist, 83, 405—414. : [2] Betechtin, A. G., 1950. Mineralogy (in Russian), pp. 823—825. | Caillere, S., and Henin. S., 1949. Transformation of Minerals of the Montmorillonite Family into 10 A Micas. Mineral Mag., 28, 606—611.

[4+] von Chroustschoff, K., 1888. Uber Kiinstlichen Magnesia-Glimmer, Tsch. Min. Petrog. Mitt, 9, 55—60.

[5] Clark, L. M., 1948. The Identification of Minerals in Boiler Deposit; Examples of Hydrothermal Synthesis in Boiler. Mineral Mag., 28, 359—366.

[6] Friedel, G., 1896. Sur un nouveau silicate artificiel. Soc. Francais Mineralogie, Bull, 19, 5—14. :

[7] Friedel, G., 1896. Sur un nouveau silicate artificiel. Soc. Francaise Mineralogie, Bull., 24, 141—159.