ДАЛЬНЕЕ И БЛИЖНЕЕ УПОРЯДОЧЕНИЕ КАТИОНОВ В СТРУКТУРАХ КАЛЬЦИЕВЫХ АМФИБОЛОВ (МЁССБАУЭРОВСКАЯ И ИНФРАКРАСНАЯ СПЕКТРОСКОПИЯ)

Abstract

Chemical composition of studied actinolites and hornblendes makes (wt %): FeO 4.31-14.43, Fe2O3 0.31-3.84; MgO 8.82-21.71, A12O3 0.56-12.23, CaO 10.58-12.29; Na2O 0.25-1.88, K2O 0.04-1.14. As a result of investigation of amphibole structure (X-ray, Mössbauer and infrared methods) long- and short range ordering of cations was established in Ml, M2, M3 sites. It is experimentally proved that when dealing with IR spectra of calcic amphibole it is necessary to introduce coefficients for normalizing integral intensity of N, I and V groups of absorption bands of OH ion stretching vibration, coordinated with triple groups of divalent cations, di- and trivalent cations, cations and vacancies, respectively (hN:hI:hV = 1 : 0.56 : 0.10). The long range ordering is seen in preferential Fe2+ occupancy of M3 site [the ordering schemes arc: Fe(M3) > Fe(M2) ≥ Fe(M1), Fe(M3) > Fe(Ml) > Fe(M2)], trivalent cations prefer (2M1 + M3) sites, Mg, Mn and Ni (but not Fe2+) occupy M4 sites, free from Ca and Na cations. Amphiboles show the slight degree of short range ordering. In most of samples the cation distribution is close to statistical one. In some samples high R3+ content and entering of Fe3+ in M2 site result in clustering. The increase of clustering degree with R3+ growth explains the restricted solubility of trivalent cations in calcic amphibole structures. Long range ordering (increasing of xM3Fe2+) and clustering are accompanied with greater cell deformation: extending along с axis and increasing of β° respectively.