Nano-crystalline osbornite from Carbonados: Spectroscopic studies

Carbonado has been recognised as a polycrystalline aggregate of diamond since 1840 and was mined as a placer mineral in Sincoro County in Brazil. Carbonado has been recovered only from alluvial deposits in Brazil and the Central African Republic (CAR). The origin of the unusual type of polycrystalline diamond is not yet understood. In order to understand the origin of this exotic diamond aggregates, we have carried out powder-X-ray diffraction, Nuclear Magnetic Resonance and FT-IR, and TEM studies on the carbonados from Brazil as well as CAR. While our data on the chemical and trace elements analyses agree with the earlier data, there is a minor difference in the observation of presence minor minerals. We have identified few grains of osbornite (TiN) with 50 to 100 nm size, and presence of lonsdaleitea high – pressure polymorph of diamond. The presence of these two minerals has been independently and unambiguously confirmed by XRD. The NMR spectrum also show a shockinduced broadening of the diamond line centred at 34.8 ppm which is more than the chemical shift 34.5ppm of pure diamond crystal. Our observation of presence of osbornite in carbonado shows the possible extraterrestrial origin of carbonado, as this mineral is known to exist only in enstatite chondrites and achondrites. Incorporation of guest-molecules into natural zeolite mordenite P. SIMONCIC AND TH. ARMBRUSTER Thermochemistry Facility, Department of Chemical Engineering and Materials Science, University of California at Davis, USA (psimoncic@ucdavis.edu) Laboratory for chem. and mineral. Crystallography, University of Bern, Switzerland (thomas.armbruster@krist.unibe.ch)