Mg-kalcit i dolomit iz belog mermera ležišta Krečana - Venčac, deo I: rendgenska ispitivanja

Abstract

With the X-ray powder diffraction analysis there were indiced powder diffraction patterns and determined qualitative, semiquantitative sample contents. Sample-1 contain Mg-calcite (1) (95%), dolomite (4%) and quartz (1%). Sample-2 contain Mg-calcite (2) (79%), quartz, feldspars, clay minerals and micas, and insignificant dolomite (1,5%). Quartz, feldspars and clay minerals-micas are probably of equally content with about 6-7%. There were calculated following unit cell dimensions: Mg-calcite (1): ao = 4,966(2)Å, co = 16,96(1)Å; Vo = 362,1(4)Å3; co/ao = 3,415; dolomite: ao = 4,791(3)Å, co = 15,95(2)Å; Vo = 317,1(4)Å3; co/ao = 3,329; Mg-calcite (2): ao = 4,9791(9)Å, co = 17,025(5)Å; Vo = 365,5(1)Å3; co/ao = 3,419; From calculated unit cell dimensions of all of these minerals it can be seen that there were partly exchanging of Ca2+ with Mg2+ and/or Fe2+, which are of smaller ionic radius than Ca2+. At Mg-calcite (1) 5,14 mol.% CaCO3 exchanged with MgCO3, while at Mg-calcite (2) 1,86 mol.%. Difference of 3,28 mol.% is related to the submicroscopic intergrowths and exsolutions of dolomite in Mg-calcite (1), and which were destroyed in Mg-calcite (2). At metamorphic Mg-calcite there did not came to distortion of the octahedra, because there were obtained almost equally MgCO3 contents through ao, co, Vo and co/ao. At dolomite it was established considerable deficit of the CaCO3 component.