engleski

Rietveld refinement of augite from basaltic andesite from Donje Jesenje (Croatia)

In the north-western part of Croatia several smaller bodies of volcanic rocks have been reported and one of these is in the vicinity of the village Donje Jesenje where samples of basaltic andesite have been found. In thin sections this rock show porphyritic to glomeroporphyritic textures with phenocrysts of clinopyroxene and plagioclase. Crystallochemical characteristics of clinopyroxenes depends on petrology of the host rock, so crystallochemical data obtained experimentally could provide useful information on conditions of their crystallization. Crystal chemistry of pyroxene from Donje Jesenje was studied combining X-ray diffraction and Rietveld structural refinement with an electron microprobe analysis. According to the results of chemical analysis investigated clinopyroxene is augite having formula (Na0.02Ca0.79Mn0.01Fe2+0.19Mg0.92Ti0.01Fe3+0.01Al0.05)VI (Si1.94Al0.06)IVO6. Based on discrimination diagrams its chemical composition corresponds to the composition of clinopyroxenes from orogenic basalts. Rietveld refinement was performed by GSAS software. The monoclinic structure (C2/c) with lattice constants a=9.744(1) Ĺ, b=8.918(1) Ĺ, c=5.262(2) Ĺ, b=106.45(1)°, V=438.53Ĺ3 was refined to Rp=0.0591 and Rwp=0.0762. Interatomic distances as well as M1 site volume indicate that augite crystallized at low-pressure (less than 10 kbar).

augite; basaltic andesite; Donje Jesenje; Croatia

nije evidentirano