Phase composition of iron compounds in the products of annealing of the tertiary basaltic rock from Góra Obłoga (the lower Silesia, Poland)

The work presents results of the research on thermal transformations of iron minerals which are present in basalt rock from Góra Obłoga in Pogórze Złotoryjskie District. The rock under study shows microporphyric texture and compact microstructure and contained: olivine, augite, diopside, plagioclases, serpentines, zeolites, apatite and also opaque minerals (oxides). The basalt was annealing within the temperature range between 573-1473 K, in air, and then, microscopic observations, X-ray diffraction as well as Mössbauer spectroscopy measurements were performed. During the heat treatment of the rock it was found that the content of olivine and augite was gradually decreasing due to progressive oxidation of iron compounds, resulting in formation of magnetite and hematite. The comparison of the results of thermal Mössbauer spectral analysis showed that transformation of iron minerals occurred already under conditions when the basic rock mass underwent only insignificant changes.