ALBERT

Description: This work presents a study of an unusual synthetic diamond sample, where calcite is the main phase in addition to diamond. Using Raman spectroscopy it can be shown that in addition to diamond carbon forms four different generations: highly ordered graphite-II, lower ordered graphite-I as spandrel between different mineral grains, weakly-ordered carbonaceous material as graphite-III and the hexagonal diamond lonsdaleite (here graphite-IV) as last formation in calcite. Graphite-III can be found mainly in the calcite body. According to the fine dispersion of this carbonaceous material and the arrangement on grain boundaries, we assume that carbon was dissolved in the calcite melt, and that by the activated state of carbon in the calcite melt the formation of diamond is favored near 1760°C, and 6.8 GPa. Lonsdaleite as minor phase may have been formed as an longlived intermediate state under standard conditions between graphite and diamond. Evidence shows that there are two different lonsdaleite phases (possibly hexagonal and monocline) present. The prevailing diamond is characterized by the first-order Raman line at 1333 cm-1. However, there are also present diamonds with the first-order Raman line down to 1310.6 cm-1, corresponding to 13C = 0.511. Significantly there is the strong decrease of the optical damage threshold with increase of the 13C content.

Description: In this contribution, we show that in miarolitic pegmatites during the crystallization of water-rich melts, samples of these mineral-forming melts were trapped in the form of water-rich melt inclusions, preserved primarily in quartz. The bulk concentration of water and the temperature are the system-determining parameters since from their analysis it follows that these melt inclusions depict pseudo-binary solvus curves in the coordinates of temperature and water concentration. Furthermore, using reduced coordinates (H2O/H2Ocrit vs. T/Tcrit) most melt inclusions of the studied pegmatites plot very well in a standardized and reduced solvus curve. The existence and formation of such uniform solvus curves is an expression of crystallization processes under nearly equilibrium conditions. However, many trace and some principal elements of the melt inclusions trapped near the solvus crest [H2O/H2Ocrit from 0.5 to 1.5 and T/Tcrit 〉 0.95] show unusual distributions, with very well-defined Gaussian and/or Lorentzian curves, characterized by defined area, width, offset, and height. This has been shown in many natural examples obtained from pegmatites. Only the offset values represent near-equilibrium conditions and corresponding element concentrations, which are equivalent to the regional Clarke number (Clarke number or Clarke is the relative abundance of a chemical element, typically in the Earth's crust). We interpret these distributions as explanation for some extraordinary-chemical properties in this critical region: principally extremely high diffusion rates, low dynamic viscosity and extremely low surface tension. Near the critical point, we have both space and time-related non-equilibrium and equilibrium processes close together. Furthermore, we can show that the Gaussian and Lorentzian distribution are first approximations of the specific element distribution because at the critical point the enrichment of some elements reaches such an extent that the Gaussian and/or Lorentzian curves degenerate into a vertical line (are asymptotic to the concentration axis), which is determined by the maximum solubility of a species in the supercritical melt-water system. The highest concentration of Be, as an example, was observed in Ehrenfriedersdorf melt inclusions: 71490 ppm Be.