Microstructures in Siderite
Abstract
Transmission Electron Microscopy (TEM) is a new technique in the study of internal structure of minerals. Siderite minerals from two localities are selected for investigation with TEM, coupled with EDX microanalysis and optical methods. The microstructures present are similar to those observed in other carbonates. The major microstructural features are the curving and branching ribbons in siderite regions and lath-like defects in calcitic grains present in Erzberg siderite. These laths are found dolomitic in structure. Similar microstructures have already been reported in saddle dolomites (Barber et al., 1985). Small calcite structured precipitates were encountered in the calcite grains, where iron concentration exceeds the already reported solubility limit. The occurrence of "c" type spots in the calcitic structure and their presence in more than one equivalent directions is also reported in this paper.
References
Barber, D.J. & Khan, M.R., 1987. Composition induced microstructures in rhombohedral carbonates. Min. Mag. 51, 71-86.
Barber, D.J., Reeder, R.J, & Smith, D.J., 1985. A TEM. microstructural study of dolomite with curved crystal faces (saddle dolomite). Contrib. Mineral. Petrol. 91, 82-92.
Barber, D.J. & Wenk, H.R. 1984. Microstructures in carbonates from Alno and Fen carbonatites. Contrib. Mineral. Petrol. 88, 233-245.
Deer, W.A., Howie, R.A. and Zussman, J., 1962. Rock forming minerals, Vol. 5: non silicates. Longmans: London.
Goldsmith, J.R., Graf, D.L., Witters, J. & Northrup, D.A., 1962, Studies in the system CaCO3 – MgCO3 – FeCO3: (1) Phase relation; (2) a method for major element spectrochemical analysis; (3) composition of some ferroan dolomites. J. Geology, 70, 659-688.
Khan, MR. & Ishaq, M. 1988. Crystallography of carbonates and the occurrence of "c" and "d" type superstructures in calcite and dolomite-type compounds. J. Sci. and Tech. Peshawar University (in press).
Khan, M.R. & Barber, D.J. 1988. A TEM Microstructural Study of Smithsonite. J. of Engin. and Applied Sci. N.W.F.P. Univ. of Engineering and Technology, Peshawar (in press).
Khan, M.R. 1987. A TEM Microstructural study of natural and synthetic rhombohedra1 carbonates. Thesis, Ph.D. (unpubl.), Univ. Essex, U.K.
King, A.H., Fu, Rong Chen, Reeder, R.J. & Barber, D.J., 1984. Calculated images of dolomite-calcite interfaces features identification in saddle dolomite. Proc. of the 42nd. Annual Meeting of the Electron Microscopy Soc. Am. 586-587.
Kucha, H. & Weizorek, A., 1984. Evidence of Superstructuring in Ankerites. T.M.P.M. Tschermaks Min. Petr. Mitt. 32 247-258.
Gundersson, S.H. & Wenk, H.R., 1981. Hetrogeneous microstructures in oolitic carbonates. Am. Mineral. 66, 789-800.
Peacor, D.R., Essene, E.J. & Gains, A.M., 1987. Petrological and crystal chemical implications of cation order/disorder in kutnahorite [ CaMn (CO3), 1. Am. Mineral. 72, 319-328.
Reeder, R.J. & Prosky, J.L., 1986. Composition sector zoning in dolomite. J. Sed. Petrol. 56, 237-247.
Reeder, R.J., 1982. Crystal growth defects in sedimentary carbonate minerals. Estudios. Geol. 38, 179-183.
Reeder, R.J. & Wenk, H.R., 1979a. Microstructures in low temperature dolomites. Geophy. Res. Lett. 6, 77-80.
Reeder, R.J. & Wed, H.R., 1979b. Modulated structures in sedimentary dolomites. In: (Cowly, J.M. et al. Eds.) Modulated structures, Am. Inst. Phys. New York. 330-332.
Rosenberg, P.E., 1963a. Subsolidus relations in the system CaCO3-FeCO3. Am. J. Sci. 261, 683-490.
Van Tendeloo, G., Wenk, H.R. & Gronsky, R., 1985. Modulated structures in calcian dolomite: A study by Electron Microscopy. Phy. Chem. Minerals. 12, 333-341.
Wenk, H.R., Baxber, D.J. & Reeder, R.J., 1983. Microstructures in carbonates. In: (R.J. Reeder, Ed.). Carbonates: Mineralogy and Chemistry. Reviews in Mineralogy. 11, 301-367. Min. Soc. Am.
