Mn-bearing eleonorite from Hagendorf South pegmatite, Germany: crystal structure and crystal-chemical relationships with other beraunite-type phosphatesстатья
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Дата последнего поиска статьи во внешних источниках: 10 августа 2018 г.
Аннотация:Mn2+-bearing eleonorite from the Hagendorf South pegmatite situated south of Waidhaus, Upper Palatinate, Bavaria, Germany was study based on single crystal X-ray analysis, Mn and Fe K-edge XANES spectroscopy, as well as IR spectroscopy. According to spectroscopic data, all Mn is bivalent, and all Fe is trivalent. The empirical formula of the mineral is (Mn0.582+Zn0.13Mg0.04Fe5.243+)(Sigma 5.98)(PO4)(4)(H2O,OH,O)(11). The monoclinic unit-cell parameters are: a = 20.832(3) angstrom, b = 5.1569(3) angstrom, c = 19.200(2) angstrom, beta = 93.01(1)degrees; space group C2/c . The structure was refined to R-1 = 5.20% in anisotropic approximation using 1994 reflections with I > 3 sigma(I). Despite in most beraunite-group minerals M1-site demonstrates selective accumulation of bivalent cations, in Mn-bearing eleonorite Mn2+-cations are disordered between octahedral sites without statistical predominance anywhere; all octahedral M (1-4)-sites are predominantly occupied by Fe3+. M1-site is half-occupied by Fe3+ and contains subordinate Mn2+ and minor Zn2+ and Mn2+. Based on the new data we suppose that Mn-bearing eleonorite was formed as a secondary phase as a result of oxidation of a primary Mn-bearing beraunite-group mineral in with Mn2+ was initially distributed between different M sites.