Synthesis, crystal structure and crystal chemistry of ferri-clinoholmquistite, ?Li2Mg3Fe3+2Si8O22(OH)2

This work reports the synthesis of ferri-clinoholmquistite, nominally square(Li2)(Mg3Fe23+)Si8O22(OH)(2), at varying f(O2) conditions. Amphibole compositions were characterized by X-ray (powder and single-crystal) diffraction, microchemical (EMPA) and spectroscopic (FTIR, Mossbauer and Raman) techniques. Under reducing conditions (less than or equal to NNO+1, where NNO = Nickel-Nickel oxide buffer), the amphibole yield is very high (>90%), but its composition, and in particular the FeO/Fe2O3 ratio, departs significantly from the nominal one. Under oxidizing conditions (less than or equal to NNO+1.5), the amphibole yield is much lower (