| Abstract: | Graphite-bearing rocks and graphites from the Precambrian metamorphic sequence of the Pestpaksha ore occurrence, Murmansk district, have been studied by the X-ray method. It was determined that the rocks have a complex polycomponent composition. Graphite is associated with garnet-quartz, pyroxene-amphibole, and biotite-quartz with an admixture of pyrrhotite, kyanite, chlorite, and other minerals. In terms of mineral composition, the studied samples are subdivided into five groups. The structural characteristics of graphite—parameters a 0 and c 0, the degree of structural perfection (U), the content of rhombohedral phase (R), and others—were found to be different for each group. The U value varies from 1.04 to 1.56 (with predominant values from 1.4 to 1.5), while the content of rhombohedral phase in samples is no more than 18%. This fact indicates a relatively high 3D order, which is typical of graphites from metamorphic rocks. Graphites from metasomatites have the lowest U value, while those from weathering zones are characterized by a small value of the coherent scattering domain (CSD). It was established that interplanar spacing d 002 of graphite correlates with depth, while the degree of ductility and flexibility of the graphite is defined by conditions of its retrograde metamorphism. |
