engleski

SOME CARBONATE MINERALS FROM MACEDONIA: ANALYTICAL APPLICATION OF THEIR FT IR SPECTRA AND POWDER XRD PATTERNS

As a part of the broader research of the structural and spectroscopic characteristics of metal minerals originating from Macedonia we report the results of the analytical application of the FT IR spectra and the powder XRD patterns of the carbonate minerals calcite (CaCO_3), siderite (FeCO_3) and aragonite (CaCO_3). As is known calcite and siderite crystallize in the hexagonal system, while aragonite is orthorhombic. The local symmetry of the CO_3^2^- ions in the structure of calcite type is D_3 and in aragonite is C_s. The lower local symmetry of the CO_3^2^- ions in the latter case causes the appearance (around 1084 cm^-^1) of the v_1 mode in its IR spectrum. Since carbonate minerals, especially the polymorphic forms of calcite and aragonite, may appear in common minerals, it is advantageous to have a rapid and simple method for detecting impurities of these minerals in one another. The appearance of the 1084 cm^-^1 band in the spectrum of aragonite (absent in the spectrum of calcite) enabled us to detect the presence of aragonite in calcite whereas the higher frequency of the v_4 mode in the spectrum of calcite (733 cm^-^1) than in aragonite (712 cm^-^1) made it possible to use their infrared spectra for detecting impurities of calcite in aragonite. The powder X-ray diagrams of these minerals were also examined with the same goal in mind. The symmetry-caused similarity between the infrared spectra of calcite and siderite made impossible their use for detecting of the presence of calcite in aragonite and vice versa and only their XRD patterns could be used.

Calcite; aragonite; mineral analysis; FT IR spectroscopy

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