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Composition-induced microstructures in rhombohedral carbonates

Published online by Cambridge University Press:  05 July 2018

D. J. Barber  and
M. Riaz Khan
D. J. Barber
Affiliation:
Physics Department, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ
M. Riaz Khan
Affiliation:
Physics Department, University of Essex, Wivenhoe Park, Colchester, Essex CO4 3SQ
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Abstract

Recent TEM observations of two-phase microstructures and associated crystal defects in selected, rare dolomites have been extended to calcite-structured (R3̄c) carbonates and to other natural and synthetic carbonates that crystallize with the dolomite (R3̄) structure. The samples included siderites (FeCO3), smithsonites (ZnCO3), ankerites (Ca[Mg,Fe](CO3)2), and kutnahorites (Ca[Mn,Fe](CO3)2).

TEM methods show that the forms of second phases which result from the presence of common, divalent, metallic impurities are morphologically similar in R3̄c and R3̄ carbonates and occur more widely than hitherto realized. The most common form consists of thin ribbons of second phase which are coherent with and have the same crystallographic orientation as the host carbonate. Another form of microstructure, manifest as modulations in diffraction contrast, appears to be associated with incipient breakdown of single-phase carbonate. The results of extensive TEM/EDS microanalyses show that in siderite and ankerite the formation of ribbons is promoted by Ca impurity or Ca excess (with respect to R3̄c stoichiometry). In smithsonite, Cu and Ca impurities can play similar roles in relation to modulated microstructures. In kutnahorites, the perfection of grains and the absence of second-phase effects is strongly dependent on the ratio of Fe to Mn but is also affected by Ca in excess of the stoichiometric requirement. Electron diffraction results from several of the minerals show c-type spots, which can be interpreted as indicating ordering within basal layers of cations.

The results show that, by correlating analytical TEM data with the study of second phases and incipient two-phase microstructures, it should be possible to determine the limits of solid solubility in carbonate systems.

Keywords

microstructuresrhombohedral carbonatessideritesmithsoniteankeritekutnahorite.
Type
Electron Microscopy in Mineralogy and Petrology
Information
Mineralogical Magazine , Volume 51 , Issue 359 , March 1987 , pp. 71 - 86
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1987

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References

Barber, D.J. and Wenk, H. g. (1984) Contrib. Mineral. Petrol., 88, 233-45.CrossRefGoogle Scholar
Reeder, R.J. and Smith, D.J. (1985) Ibid. 91, 82-92.Google Scholar
Barron, B.J. (1974) Ibid. 47, 77-80.Google Scholar
Bickle, M.J. and Powell, R. (1977) Ibid. 59, 281-92.Google Scholar
Cliff, G. and Lorimer, G.W. (1975) J. Microsc., 103, 203-7.CrossRefGoogle Scholar
Effenberger, H., Mereiter, K. and Zemann, J. (1981) Z. Kristallogr., 156, 233-43.Google Scholar
Goldsmith, J.R. (1960) J. Geol., 68, 103-9.CrossRefGoogle Scholar
Goldsmith, J.R. (1983) In Rev. in Mineralogy U (R. J. Reeder, ed.) Mineral. Soc. America.Google Scholar
Gittins, J. (1979) Contrib. Mineral. Petrol., 69, 1-4.CrossRefGoogle Scholar
Gunderson, S.H. and Wenk, H.R. (1981) Am. Mineral., 66, 789-800.Google Scholar
King, A.H., Chen, F.R., Reeder, R.J. and Barber, D.J. (1984) Proc. 42nd Mtng EMSA (G. W. Bailey, ed.) San Francisco Press, Inc.Google Scholar
Kucha, H. and Wieczorek, A. (1984) Tschermaks Mineral. Petr. Mitt., 32, 247-58.CrossRefGoogle Scholar
Lloyd, R.V., Lumsden, D.N. and Gregg, J.M. (1985) Geochim. Cosmochim. Acta, 49, 2565-8.CrossRefGoogle Scholar
Puhan, D. (1984) Contrib. Mineral. Petrol., 87, 98-9.CrossRefGoogle Scholar
Radke, B.M. and Mathis, R.L. (1980) J. Sed. Petrol., 50, 1149-68.Google Scholar
Rceder, R.J. (1981) Contrib. Mineral. Petrol., 76, 148-57.Google Scholar
Rceder, R.J. (1983a) In Rev. in Mineralogy 11 (R. J. Reeder, ed.) Mineral Soc. America.Google Scholar
Rceder, R.J. (1983b) Estudios Geologicos, 38, 179-83.Google Scholar
Rceder, R.J. and Wenk, H.R. (1979a) Geophys. Res. Lett. 6, 77-80.Google Scholar
Rceder, R.J. -and Wenk, H.R. (1979b) In Modulated Structures--1979 (J. M. Cowley et al., eds.) American Inst. Physics.Google Scholar
Rosenberg, P.E. and Foit, F.F. (1979) Geochim. Cosmochim. Acta, 43, 951-5.CrossRefGoogle Scholar
Van Tendeloo, G., Wenk, H.R. and Gronsky, R. (1985) Phys. Chem. Minerals, 12, 333-41.CrossRefGoogle Scholar
Von Eckermann, H. (1948) Sverig. Geol. Undersok., Ser. Ca., No. 36.Google Scholar
Wenk, H.R. and Fusheng, Z. (1985) Geology, 13, 457-60.2.0.CO;2>CrossRefGoogle Scholar
Wenk, H.R. and Fusheng, Z. and Maurizio, R. (1978) Schweiz. Mineral. Petrogr. Mitt., 58, 97-100.Google Scholar
Wenk, H.R. and Fusheng, Z. -Barber, D.J. and Reeder, R.J. (1983) In Rev. in Mineralogy 11 (R. J. Reeder, ed.) Mineral. Soc. America.Google Scholar
Wood, J.E., Williams, D.B. and Goldstein, J.I. (1984) J. Microsc., 133, 255-74.CrossRefGoogle Scholar
Zak, L. and Povondra, P. (1981) Tschermaks Mineral. Petr. Mitt., 28, 55-63.Google Scholar