Structure and Defects in Natural Ballas-Type Diamonds: a Case Study
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ucture and Defects in Natural Ballas-Type Diamonds: a Case Study A. A. Shiryaeva, b, *, A. F. Khokhryakovc, V. N. Reutskyc, and T. I. Golovanovab aFrumkin
Institute of Physical Chemistry and Electrochemistry, Russian Academy of Sciences, Moscow, 119071 Russia of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences, Moscow, 119017 Russia cV.S. Sobolev Institute of Geology and Mineralogy Siberian branch of Russian Academy of Sciences, Novosibirsk, 630090 Russia *e-mail: [email protected], [email protected] bInstitute
Received April 29, 2020; revised June 29, 2020; accepted June 29, 2020
Abstract—Structure, defects and inclusions in natural polycrystalline ballas-type diamonds are studied by complementary techniques: Scanning Electron microscopy, cathodo- and photoluminescence, X-ray diffraction, radiography and fluorescence, infra-red spectroscopy and carbon isotope analyses. Peculiarities of internal structure of some of the samples are explained by growth of the diamonds as volume-filling dendrites. Similarities of structure and mineralogy of trapped inclusions between ballas-type diamonds with fibrous and cuboid diamonds are established. However, significant differences between growth mechanisms of all these varieties exist and are possibly explained by variations in carbon supersaturation and diamond wettability by growth medium. Keywords: polycrystalline diamond, ballas, inclusions, point defects, amber defects, carbon isotopic composition DOI: 10.1134/S0016702920120058
INTRODUCTION Polycrystalline diamonds and intergrowths of single diamond crystals are rather common in nature. However, detailed studies of their internal structure and defects are relatively rare in comparison with huge number of works describing single crystals. Morphological classification of natural diamonds developed by Yu.L. Orlov (Orlov, 1977) is perhaps too coarse in description of common single crystals (termed variety I), but provides a rather detailed ranking of polycrystalline aggregates. In many cases, details of formation process and structure of polycrystalline diamonds remain poorly understood. In particular, diamond varieties like ballas attract considerable attention due to their high performance in industrial applications, but considerable debates about structural variability of these diamonds still exist (see Lux et al., 1997 for review). In this work, we present results of investigation of four natural diamonds belonging to varieties VI (ballas) and VII (intergrowths of few single crystals) in Orlov’s classification using complementary analytical methods addressing structural properties, impurities and defects. EXPERIMENTAL METHODS The samples were obtained commercially as “ballases” and their provenance is unknown, but Brazil is
a possible source. Morphology and general structural data of whole crystals was addressed using Scanning Electron microscopy (SEM) and X-ray Laue imaging. SEM investigation was performed using JSM-6510LV (JEOL Ltd) microscope. X-ray Laue patterns wer
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