Synthesis and characterisation of ferri-clinoferroholmquistite, Li (sub 2) (Fe (super 2+) (sub 3) Fe (super 3+) (sub 2) )Si (sub 8) O (sub 22) (OH) (sub 2)
Synthesis and characterisation of ferri-clinoferroholmquistite, Li (sub 2) (Fe (super 2+) (sub 3) Fe (super 3+) (sub 2) )Si (sub 8) O (sub 22) (OH) (sub 2) (in Special issue dedicated to the memory of Luciano Ungaretti, Maria Chiara Domeneghetti (prefacer))
European Journal of Mineralogy (April 2003) 15 (2): 321-327
Ferri-ferroclinoholmquistite is found experimentally to have a very restricted T stability; an almost monophase amphibole is obtained at 500 degrees C over a wide P range (1-7 kbar), whereas a Li-bearing pyroxene becomes predominant for T > or = 600 degrees C. Ferri-ferroclinoholmquistite has a 9.489, b 18.036, c 5.313 Aa, beta 101.59 degrees , V 890.80 Aa (super 3) , space group C2/m. IR spectra in the OH-stretching region show the presence of a single sharp band at 3614 cm (super -1) , which is assigned to the Fe (super 2+) -Fe (super 2+) -Fe (super 2+) trimer at the M1M1M3 octahedra and a small satellite band at 3644 cm (super -1) assigned to Li at M3. Moessbauer spectra can be fitted to three doublets assigned to Fe (super 3+) at M2, Fe (super 2+) at M1 and Fe (super 2+) at M3, with a calculated Fe (super 3+) /Fe (super 2+) ratio of 2/3, suggesting a composition close to the nominal one. The spectroscopic data show that the structure has a strongly ordered cation distribution.