Scientia Sinica

No, |] TU: PRELIMINARY RESULTS ON HYDROTHERMAL SYNTHESIS OF BRITTLE MICAS 181

In Table 2 are listed the spacings and intensities of the synthetic margarite, together with those of a natural margarite. The average index of refraction of artificial margarite is 1.615, which is slightly lower than that of the natural mineral, This may be due to the extremely fine size of the synthetic product.

~ Table II. Powder Diagrams of the Synthetic Margarite and the Natural Magarite from Chester, Mass., U.S.A, (Radius of Camera 57.3 mm, FeK, 1.932.)

Synthetic Margarite Margarite, Chester, eae No. d Observed I | d Observed I 1 |Indistinct DEAT. Vw 2 4.82 Vw 4.71 Vw 3 4.422 s 4.388 | Ww 4 3.566 VW 3.645 S 5 3.203 $ 3.186 VS 6 2.974 W 2.898 W 7 2.808 S ‘ 2.777 Ss 8 2.681 W 2.683 W 9 2.533 VS 2.529 S 10 2.425 S 2.408 S 11 2.094 S 2.078 Br 12 1.916 W 1.913 VS = 1s) 1.780 Vw 1.757 | WwW 14 1.684 W 1.673 | Ww 15 1.601 W 1.592 S 16 1.483 VS 1.486 W 17 1.465 S

ee ._ VS=very strong, S=strong, W—=weak, VW very weak, Br=broad

GEOLOGICAL CONSIDERATIONS

That margarite, the Ca brittle mica, was hydrothermally prepared in our experiments tends to indicate that brittle micas might have formed at least partly in nature under non-stress conditions. Betechtin”! in his “Mineralogy”