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On sub-micrometre inclusions in diamond coat: crystallography and composition of ankerites and related rhombohedral carbonates

Published online by Cambridge University Press:  05 July 2018

J. C. Walmsley  and
A. R. Lang
J. C. Walmsley
Affiliation:
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
A. R. Lang
Affiliation:
H. H. Wills Physics Laboratory, University of Bristol, Tyndall Avenue, Bristol BS8 1TL, UK
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Abstract

Crystallographic studies of micro-inclusions in diamond coat, carried out by analytical electron microscopic techniques, show that structures possessing rhombohedral symmetry form a significant fraction of the population of well-crystaUised particles. They are, however, less frequent than apatite or biotite, which were identified earlier by the same investigative methods. Thin-foil specimens of diamond coat were prepared by mechanical fine-polishing, and subsequently ion-beam milling, sawn and polished plates of coated diamonds oriented parallel to (100) or (110). The majority of crystalline inclusions analysed were ≤0.2 p,m in diameter. Data obtained on 15 individual inclusions, including composition analysis by energy-dispersive X-ray spectroscopy, are reported and discussed. The a-axis of the hexagonal unit cell, and the c/a ratio, were determined for all specimens, and are believed to be accurate to ≈1% in most cases. In 12 out of 15 specimens, the cations with Z ≥ 11 identified comprised substantially only Mg, Fe and Ca. Values of a in these specimens ranged from 4.81 to 4.92 Å; and for three of them the space group R, corresponding to the dolomite structure, was positively identified. These crystals are classed as ankerites. Representative Mg:Fe:Ca ratios in the ankerites are 28 : 18 : 54, with cell dimensions a = 4.87 Å, c/a = 3.37. The ankerites contained small amounts of Ba, typically 1-3%, and smaller amounts of Sr, typically 0.2-2%. Three out of the 15 specimens contained >10% Ba. In two of these, Ba and Ca concentrations were roughly equal, and in one of the two, which had cell parameters a = 5.11 Å, c/a = 3.50, the space group symmetry Rc, corresponding to the calcite structure, was verified.

Keywords

ankeritecarbonatesdiamond coatinclusions
Type
Research Article
Information
Mineralogical Magazine , Volume 56 , Issue 385 , December 1992 , pp. 533 - 543
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1992

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Footnotes

*

Present address: Nuclear Electric, Berkeley Nuclear Laboratories, Berkeley, Gloucestershire GL13 9PB, UK.

References

Boyd, S. R., Mattey, D. P., Pillinger, C. T., Milledge, H. J., Mendelssohn, M., and Seal, M. (1987) Multiple growth events during diamond genesis: an integrated study of carbon and nitrogen isotopes and nitrogen aggregation state in coated stones. Earth Planet. Sci. Lett., 86, 341–53.CrossRefGoogle Scholar
Bragg, W. L. and Claringbull, G. F. (1965) Crystal Structures of Minerals, London, Bell and Sons.Google Scholar
Bruton, E. (1978) Diamonds, 2nd ed., N.A.G. Press, London.Google Scholar
Chang, L. L. Y. (1965) Subsolidus phase relations in the systems BaCO3-SrCO3, SrCO3-CaCO3 and BaCO3- CaCO3. J. Geol., 73, 346–68.CrossRefGoogle Scholar
Chrenko, R. M., McDonald, R. S., and Darrow, K. A. (1967) Infra-red spectra of diamond coat. Nature, 213, 474–6.CrossRefGoogle Scholar
Cliff, G. and Lorimer, G. W. (1975) The quantitative analysis of thin specimens. J. Microsc., 103, 203–7.CrossRefGoogle Scholar
Custers, J. F. H. (1950) On the nature of the opal-like outer layer of coated diamonds. Am. Mineral., 35, 51–8.Google Scholar
Graf, D. L. (1961) Crystallographic tables for the rhombohedral carbonates. Ibid., 46, 1283-316.Google Scholar
Guthrie, G. D. Jr., Veblen, D. R., Navon, O., and Rossman, G. R. (1991) Submicrometer fluid inclusions in turbid-diamond coats. Earth Planet. Sci. Lett., 105, 1–12.CrossRefGoogle Scholar
Harris, J. E. (1980) Recent research—the diamond geologists’ tale. Industrial Diamond Review, 40, 470–7.Google Scholar
Howie, R. A. and Broadhurst, F. M. (1958) X-ray data for dolomite and ankerite. Am. Mineral., 43, 1210–4.Google Scholar
Kamiya, Y. and Lang, A. R. (1965) On the structure of coated diamonds. Phil. Mag., 11, 347–56.CrossRefGoogle Scholar
Kesson, S. E. and Ringwood, A. E. (1989) Slab-mantle interactions. 2. The formation of diamonds. Chem. Geol., 78, 97–118.CrossRefGoogle Scholar
Lang, A. R. and Walmsley, J. C. (1983) Apatite inclusions in natural diamond coat. Phys. Chem. Mineral., 9, 6–8.CrossRefGoogle Scholar
Lang, A. R. and Walmsley, J. C. Moore, M., and Walmsley, J. C. (1992) Diffraction and imaging studies of diamond. In The Properties of Natural and Synthetic Diamond (J. E. Field, ed.) Chapter 5, Academic Press, London.Google Scholar
Machado, W. G., Moore, M., and Woods, G. S. (1985) On the dodecahedral growth of coated diamonds. J. Crystal Growth, 71, 718–27.CrossRefGoogle Scholar
Meyer, H. O. A. (1987) Inclusions in diamond. In Mantle Xenoliths (P. H. Nixon, ed.), Wiley, New York, N.Y., pp. 501-22.Google Scholar
Navon, O., Hutcheon, I. D., Rossman, G. R., and Wasserburg, G. J. (1988) Mantle-derived fluids in diamond micro-inclusions. Nature, 335, 784–9.CrossRefGoogle Scholar
Orlov, Yu. L. (1977) The Mineralogy of the Diamond, Wiley, New York.Google Scholar
Touloukian, Y. S., Kirby, R. K., Taylor, R. E., and Lee, T. Y. R. (1977) Thermal Expansion-Non-metallic Solids, Thermophysical Properties of Matter, Vol. 13, pp. 638-40, IFI/Plenum, New York-Washington.Google Scholar
Walmsley, J. C. (1981) The nature of diamond coat. M.Sc. Thesis, University of Bristol.Google Scholar
Walmsley, J. C. and Lang, A. R. (1992a) Oriented biotite inclusions in diamond coat. Mineral. Mag., 56, 108–11.CrossRefGoogle Scholar
Walmsley, J. C. and Lang, A. R. (1992b) Study of a platelet-free infilling of a crack in natural diamond: evidence for a late growth event. J. Crystal Growth, 116, 225–34.CrossRefGoogle Scholar