Letter | Published:

Exceptionally Calcic Pyralspite from South African Kyanite Eclogite

Naturevolume 212pages6869 (1966) | Download Citation



PYRALSPITE garnets with C (=Ca/Ca+Mg+Mn+Fe2+)> 0.35 are rare. Some authors1 postulate a miscibility gap between garnets of composition C < 0.35 and the ugrandite series with C > 0.70. The alternative, that garnets with 0.35<C<0.70 are stable but crystallize, under suitable physical conditions, only from rarely encountered silica-poor bulk compositions, has also been suggested2. This hypothesis is supported by the synthesis of a complete series of garnets (C = 0−1.0) between pyrope and grossularite at 30 kbars and 1,200° C (ref. 3). The synthetic garnets with C values between 0.5 and 0.7 are of particular interest because at 30 kbars and 1,600° C these compositions crystallize as clinopyroxene solid solutions4, while the paragenesis clinopyroxene + corundum is a third possibility. The essential relationships are illustrated by the equations:

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  1. 1

    Tröger, W. E., Optische Bestimmung der gesteinsbildenden Minerale (Schweizerbart'scho Verlagsbuchandlung, Stuttgart, 1956). Winchell, A. N., Elements of Optical Mineralogy, fourth ed., 2 (1951).

  2. 2

    Ford, W. E., Amer. J. Sci., 190, 33 (1915). O'Hara, M. J., Geol. Mag., 97, 145 (1960). O'Hara, M. J., and Mercy, E. L. P., Trans. Roy. Soc. Edin., 65, 251 (1963).

  3. 3

    Chinner, G. A., Boyd, F. R., jun., and England, J. L., Yearb. Carneg. Instn., 59, 87 (1960).

  4. 4

    Clark, S. P., jun., Schairer, J. F., and de Neufville, J., Yearb. Carneg. Instn., 61, 59 (1962). O'Hara, M. J., Yearb. Carneg. Instn., 62, 116 (1963).

  5. 5

    Williams, A. F., The Genesis of the Diamond (Benn, London, 1932).

  6. 6

    Sobolev, V. S., and Sobolev, N. V., Dokl. Akad. Nauk S.S.S.R., (E.S.S. translation), 158, 22 (1964).

  7. 7

    Sobolev, N. V., and Kuznetsova, I. K., Dokl. Akad. Nauk S.S.S.R., (E.S.S. translation), 163, 137 (1965).

  8. 8

    Yoder, H. S., jun., and Tilley, C. E., J. Petrol., 3, 342 (1962).

  9. 9

    Mercy, E. L. P., and O'Hara, M. J. (unpublished results).

  10. 10

    Sobolev, V. S., (ed.), Almaznye Mestorozhedniya Yakutii, Gosgeoltekhizdat, Moscow (1959). Sobolev, V. S., Rep. Twenty-first Int. Geol. Congr., 14, 72 (1960).

  11. 11

    O'Hara, M. J., Yearb. Carneg. Instn., 62, 76 (1963).

  12. 12

    Heutsch, H., Z. Krist., 86, 253 (1933).

  13. 13

    Deer, W. A., Howie, R. A., and Zussman, J., Rock Forming Minerals, 1, 95 (Longmans, London, 1962).

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  1. Grant Institute of Geology, University of Edinburgh

    • M. J. O'HARA
    •  & E. L. P. MERCY


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