Internal texture and syngenetic inclusions in carbonado

Samples of carbonado from Brazil and the Central African Republic were studied with the use of electron backscatter diffraction (EBSD) for quantitative textural analysis (QTA) and transmission electron microscopy (TEM). The grain size distribution in carbonado is either random or may be approximated by a log-normal distribution model with a mode at 6–8 μm. No bimodal distribution, as suggested previously for some carbonado samples, was observed. The crystallographic orientations of diamond grains in carbonado are quasi-random. The following minerals were identified among syngenetic mineral inclusions, enclosed in diamond grains of carbonado: garnet, apatite (including fluorapatite), phlogopite (or high-silica mica), SiO 2 , Ca-Mg-Sr- and Ca-Ba-carbonates, halides (sylvite and bismocolite BiOCl), native Ni and metal alloys (Fe-Ni, Cr-Fe-Mn, and Pb-As-Mo), oxides (FeO, Fe-Sn-O, TiO 2 , SnO 2 , and PbO 2 ), and Fe-sulfides, as well as fluid inclusions. Most of these occur over a very wide range of stability conditions. Only bismocolite, which is characteristic of the weathered crust, can be considered an entirely crustal mineral phase, which implies a possible crustal origin of the entire mineral association. Among syngenetic liquid inclusions in diamond grains comprising carbonado, silicate-carbonate ones overwhelmingly predominate. In addition to the usual silicate components, such as Si, Ti, Al, and Fe, they have Ca, K, and Cl; the latter three comprise 11.9 at.% of the only analyzed fluid inclusion.

[1]  H. Leroux,et al.  Petrogenesis of mineral micro-inclusions in an uncommon carbonado , 2011 .

[2]  O. Ohtaka,et al.  Static disorders of atoms and experimental determination of Debye temperature in pyrope: Low- and high-temperature single-crystal X-ray diffraction study , 2011 .

[3]  P. Cartigny.  Mantle-related carbonados? Geochemical insights from diamonds from the Dachine komatiite (French Guiana) , 2010 .

[4]  H. Schaeben,et al.  Texture Analysis with MTEX – Free and Open Source Software Toolbox , 2010 .

[5]  O. Safonov,et al.  Experimental model for alkalic chloride-rich liquids in the upper mantle , 2009 .

[6]  R. Wirth,et al.  Nyerereite and nahcolite inclusions in diamond: evidence for lower-mantle carbonatitic magmas , 2009, Mineralogical Magazine.

[7]  R. Wirth,et al.  Focused Ion Beam (FIB) combined with SEM and TEM: Advanced analytical tools for studies of chemical composition, microstructure and crystal structure in geomaterials on a nanometre scale , 2009 .

[8]  G. Mccall.  The carbonado diamond conundrum , 2009 .

[9]  Helmut Schaeben,et al.  A novel pole figure inversion method: specification of the MTEX algorithm , 2008 .

[10]  S. Fukura,et al.  Infrared and Raman spectroscopic observations of Central African carbonado and implications for its origin , 2008 .

[11]  A. V. Ignat’ev,et al.  First diamonds from placers in Primorie , 2006 .

[12]  M. Martins.  Geologia dos diamantes e carbonados aluvionares da bacia do rio Macaúbas (MG) , 2006 .

[13]  R. Wirth,et al.  TEM imaging and analysis of microinclusions in diamonds: A close look at diamond-growing fluids , 2006 .

[14]  G. Kurat,et al.  Experimental study of diamondite formation in carbonate-silicate melts: A model approach to natural processes , 2005 .

[15]  S. Filatov,et al.  High-pressure synthesis of α-PbO2 and its crystal structure at 293, 203, and 113 K from single crystal diffraction data , 2005 .

[16]  R. Wirth,et al.  Focused ion beam (FIB): A novel technology for advanced application of micro- and nanoanalysis in geosciences and applied mineralogy , 2004 .

[17]  E. Vicenzi,et al.  Microstructural study of synthetic sintered diamond and comparison with carbonado, a natural polycrystalline diamond , 2003 .

[18]  M. L. Chaves,et al.  Ion microprobe Pb–Pb dating of carbonado, polycrystalline diamond , 2002 .

[19]  E. Vicenzi,et al.  Chemical heterogeneity in carbonado, an enigmatic polycrystalline diamond , 2001 .

[20]  F. Brenker,et al.  The application of electron backscatter diffraction and orientation contrast imaging in the SEM to textural problems in rocks , 1999 .

[21]  C. Censier,et al.  Sedimentary processes in the Carnot Formation (Central African Republic) related to the palaeogeographic framework of Central Africa , 1999 .

[22]  E. Vicenzi,et al.  Microstructural observations of polycrystalline diamond: a contribution to the carbonado conundrum , 1998 .

[23]  S. Master.  The Kogo Structure (Equatorial Guinea) as a Possible Source Crater for the Origin of Carbonado Diamonds from Brazil and the Central African Republic , 1998 .

[24]  D. Mattey,et al.  He, Ar and C isotopes in coated and polycrystalline diamonds , 1998 .

[25]  T. Ohta,et al.  Rare-earth element patterns and carbon isotopic composition of carbonados: implications for their crustal origin. , 1996 .

[26]  T. Daulton,et al.  Radiation-Induced Diamond Formation in Uranium-Rich Carbonaceous Materials , 1996, Science.

[27]  D. P. Svisero.  Distribution and origin of diamonds in Brazil: An overview , 1995 .

[28]  A. Morawiec.  Misorientation‐Angle Distribution of Randomly Oriented Symmetric Objects , 1995 .

[29]  Kazuya Takahashi,et al.  CHEMICAL PROPERTIES OF CENTRAL AFRICAN CARBONADO AND ITS GENETIC IMPLICATIONS , 1994 .

[30]  F. Kaminsky,et al.  Rare earth element patterns of carbonado and yakutite: evidence for their crustal origin , 1993, Mineralogical Magazine.

[31]  K. Kunze,et al.  Orientation imaging: The emergence of a new microscopy , 1993 .

[32]  T. Armbruster,et al.  A combined temperature dependent57Fe Mössbauer and single crystal X-ray diffraction study of synthetic almandine: evidence for the Gol'danskii-Karyagin effect , 1992 .

[33]  Y. Matsuhisa,et al.  Constraints from noble-gas contents on the origin of carbonado diamonds , 1991, Nature.

[34]  Rory O. Moore,et al.  Pyroxene solid solution in garnets included in diamond , 1985, Nature.

[35]  JOSEPH V. Smith,et al.  Carbonado: Diamond aggregates from early impacts of crystal rocks? , 1985 .

[36]  T. Yagi,et al.  Phase boundary and transition rate of orthorhombic-cubic transformation in PbO2 , 1980 .

[37]  L. Trueb,et al.  Carbonado: Natural Polycrystalline Diamond , 1969, Science.

[38]  A. Verchovsky,et al.  CARBONADO: MORE CLUES TO A COMMON IMPACT ORIGIN FOR SAMPLES FROM BRAZIL AND THE CENTRAL AFRICAN REPUBLIC , 2009 .

[39]  Y. Litvin,et al.  Rapid growth of diamondite at the contact between graphite and carbonate melt: Experiments at 7.5-8.5 Gpa , 2003 .

[40]  M. Ozima,et al.  Radiation-induced diamond crystallization: Origin of carbonados and its implications on meteorite nano-diamonds , 1997 .

[41]  G. Voutsas,et al.  The crystal structure of BiOCl , 1993 .

[42]  T. Friedrich,et al.  Crystal structure of calcium palladium aluminium (1/1/1), CaPdAl , 1993 .

[43]  W. M. Haynes.  CRC Handbook of Chemistry and Physics , 1990 .

[44]  H. Bunge.  Three-dimensional texture analysis , 1987 .

[45]  N. N. Greenwood,et al.  Chemistry of the elements , 1984 .

[46]  H. Bunge.  Texture Analysis in Materials Science , 1982 .