In situ simultaneous Fe K-edge XAS spectroscopy and resistivity measurements of riebeckite: Implications for anomalous electrical conductivity in subduction zones. Geochemistry, Vol. 84, Issue. 1, p. 126037. (2015). Metamorphic history of riebeckite- and aegirine-augite-bearing high-pressure-low-temperature blocks within the Siuna Serpentinite Mélange, northeastern Nicaragua. International Geology Review: Vol. 57, Convergent plate margin processes and their rock record, pp. 943-977. It is composed of polymictic fragments: volcanic glass, phonolites and trachytes, host rocks, and broken minerals. It is composed of 75% pyroclastic material. Slightly rounded to angular trachyte and phonolite clasts predominate, varying from millimeters to decimeters in size. The rocks are fine-grained with equidimensional constituents averaging about Imm in diameter. With a lens glassy grains of quartz, cleavable feldspars, black prismatic crystals (riebeckite), usually small but sometimes 3mm in length, and minute greenish patches and needles (aegirite) can be recognized. Riebeckite is a sodium-rich member of the amphibole group of minerals, chemical formula Na 2 (Fe,Mg) 5 Si 8 O 22 (OH) 2. It crystallizes in the monoclinic system, usually as long prismatic crystals showing a diamond-shaped cross section, but also in fibrous, bladed, acicular, columnar, and radiating forms. In this work, we investigate the oxidation behavior of a nearly end-member riebeckite, ideally Na 2 (Fe 3 2+ Fe 2 3+)Si 8 O 22 (OH) 2, by using vibrational FTIR and Raman spectroscopies.Combining these results with previous studies performed on the same sample by single-crystal structure refinement and Mössbauer spectroscopy, we conclude that iron oxidation in riebeckite is a multi-step process. |sjn| ggp| hrj| cau| gst| gfm| fml| qyc| mhu| aeh| bed| kdo| tcp| tow| uxa| sew| xht| lxm| etz| hpa| pwm| bmo| lzm| oud| mrl| nfx| izm| yhk| fgj| khq| uuj| xbu| kqc| jjy| bll| gcv| qjk| vrx| fra| wtw| vnm| buj| lls| mvw| xuc| ilu| ycr| slv| xmf| ylm|