Diamonds in the products of Tolbachik fissure eruption 2012-2013, Kamchatka

Diamonds were found in porous andesite basalt of the Tolbachik Fissure Eruption 27.12.2012-9.10.2013. They are well-formed, isometric, well-faceted crystals with sharp ribs, of up to 700 microns of size with approximately equal faces of the octahedron and cube. As additional facets (in the order of occurrence), rhombic dodecahedron {110}, tetragontrioctaeder {131}, and trigontrioctaeder {332} are encountered. The cathodoluminescence studies revealed a clear sectorial heterogeneity in crystals caused by a combination of pyramids of growth of the octahedron and cube faces. Partially, the Tolbachik diamonds are presented by the twins grown on the spinel law. In the face pits and cavities, the inclusions of Mg-Fe- and Fe silicates, Ca-Mg silicates, aluminosilicates, sulfates, iron oxides, native metals and alloys of Fe, Ni-Cu, and Cu-Sn-Fe were observed. Study of the grains phase was carried out by X-ray and Raman spectroscopic methods. Calculated from the X-ray unit cell parameter was 0.3556 (3) nm. Raman spectrum is presented by a single strong line of 1332 cm -1, with A1/2 (FWHN) = 5-7 см -1, corresponding to the diamond. The IR absorption spectra showed the only lines at 1345 and 1130 cm -1, corresponding to the C structural defects. Some of these defects are in the positive charge state N+ (line at 1332 cm -1). Thermal oxidation of observed diamonds begins at a relatively low temperature for diamond (740-750 ° C), and the culmination starts at 920-960° C, characteristic for kimberlite diamonds. Poorly differentiated geochemical association of impurities and very stable isotopic composition of carbon, not lower than 27... -22 %%, characterize the studied samples. Uniqueness of crystal morphology, spectroscopic, mineralogical, geochemical and isotopic properties suggest to refer Tolbachik diamonds to a previously unknown volcanic-eruption or Tolbachik genetic type.