Hostname: page-component-78c5997874-4rdpn Total loading time: 0 Render date: 2024-11-18T07:37:05.303Z Has data issue: false hasContentIssue false
  • English
  • Français

Mineral chemistry and paragenesis of astrophyllite from Egypt

Published online by Cambridge University Press:  05 July 2018

Abdel-Fattah M. Abdel-Rahman
Abdel-Fattah M. Abdel-Rahman*
Affiliation:
Department of Geological Sciences, McGill University, 3450 University Street, Montreal, Quebec, Canada, H3A 2A7
Get access Rights & Permissions [Opens in a new window]

Abstract

Astrophyllite is a rock-forming mineral (3.4 vol.%) in the metasomatized wallrocks within 2 to 3 km of the contact with the Mount Gharib A-type complex in northeastern Egypt. In the peralkaline A-type granites of the main complex, astrophyllite occurs in accessory amounts (0.1 to 0.5 vol.%), mostly in association with arfvedsonite. Eighteen chemical analyses of astrophyllite from both rock units have been used to discuss mineral chemistry, compositional variations and isomorphism.

Substitutions in the astrophyllite unit cell [(Na,K)3Fe7Ti2Si8(O,OH)31] involve F, Ca, Mn, Zn, Mg, Nb, Zr, Sn and A1. The contents of the unit cell depart from ideal stiochiometry. Unusually high Nb contents (up to 5 wt.% Nb2O5) characterize the Egyptian astrophyllitcs. The replacement of Ti by Nb is balanced by cation vacancies (Nb5+ → Ti4+ + □). The niobophyllite-astrophyllite relationship and the structure of astrophyllite in relation to mica and biopyriboles are discussed.

Astrophyllite may have been formed at the expense of alkali amphiboles by metasomatic reactions involving Ti-Nb-rich alkaline fluids and arfvedsonite;

Most astrophyllite reported in the literature occurs in association with alkali amphiboles, particularly arfvedsonite, thus suggesting that similar metasomatic reactions were responsible for the formation of astrophyllite in many other localities in the world.

Keywords

astrophylliteA-type granitearfvedsonitemetasomatic reactionsEgypt
Type
Research Article
Information
Mineralogical Magazine , Volume 56 , Issue 382 , March 1992 , pp. 17 - 26
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2014

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

Footnotes

*

Present address: Department of Geology, Concordia University, Loyola Campus, 7141 Sherbrooke Street West, Montreal, Quebec, Canada, H4B 1R6.

References

Abdel-Rahman, A. M. (1986) Ph.D. Thesis, McGill University, Montreal, 326 pp.Google Scholar
Abdel-Rahman, A. M. (1987) Neues. Jahrb. Mineral. Abh., 157, 319–35.Google Scholar
Abdel-Rahman, A. M. and Doig, R. (1987) J. Geol. Soc. London, 144, 577–86.10.1144/gsjgs.144.4.0577CrossRefGoogle Scholar
Abdel-Rahman, A. M. and Martin, R. F. (1987) Geol. Jour., 22, 281–301.Google Scholar
Abdel-Rahman, A. M. and Martin, R. F. (1990a) Contrib. Mineral. Petrol., 104, 173–83.10.1007/BF00306441CrossRefGoogle Scholar
Abdel-Rahman, A. M. and Martin, R. F. (1990b) Can. Mineral. 28, 267–85.Google Scholar
Bailey, S. W. (1984) In Micas; Reviews In Mineralogy, 13 (S. W. Bailey, ed.), 1-12.Google Scholar
Floor, P. (1966) Leidse Geol. Medd., 36, 1–17.Google Scholar
Ganzeyev, A. A., Yefimov, A. F., and Semenova, N. G. (1969) Gcochem. Intern. 6, 295–300.Google Scholar
Gosner, B. and Reindl, E. (1934) Centr. Min., Abt. A, 161.Google Scholar
Hansen, J. (1968) Rept. 23rd Inter. Geol. Congr., Czechoslovakia, 7, 263–73.Google Scholar
Jahns, R. H. and Burnham, C. W. (1969) Econ. Geol., 64, 843–64.10.2113/gsecongeo.64.8.843CrossRefGoogle Scholar
Layne, G. D., Rucklidge, J. C., and Brooks, C. K. (1982) Mineral. Mag., 45, 149–56.10.1180/minmag.1982.045.337.17CrossRefGoogle Scholar
Macdonald, R. and Saunders, M. J. (1973) Ibid., 39, 97-111.Google Scholar
Marsh, J. S. (1975) Contrib. Mineral. Petrol., 50, 135–44.10.1007/BF00373333CrossRefGoogle Scholar
Nickel, E. H., Rowland, J. F., and Charette, D. J., (1964) Can. Mineral., 8, 40–52.Google Scholar
Peng, C.-C. and Ma, C.-S. (1963) Sci. Sinica, 12, 272.Google Scholar
Semenov, Ye. I. (1956) Dokl. Akad. Nauk. USSR, 108, 933–6.Google Scholar
Veblen, D. R. and Burnham, C. W. (1978) Am. Mineral., 63, 1053–73.Google Scholar
Veblen, D. R. and Burnham, C. W. Busck, P. R., and Burnham, C. W. (1977) Science, 198, 359–65.10.1126/science.198.4315.359CrossRefGoogle Scholar
Wallace, G., Whalen, J. B., and Martin, R. F. (1990) Can. Mineral., 28, 251–66.Google Scholar
Woodrow, P. J. (1967) Acta Crystallogr., 22, 673-8.10.1107/S0365110X67001331CrossRefGoogle Scholar