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Giovanni Ferraris, M. Prencipe, E. Sokolova, V.M. Gekimyants, E.M. Spiridonov
Hydroxylclinohumite, a new member of the humite group: Twinning, crystal structure and crystal chemistry of the clinohumite subgroup
Hydroxylclinohumite Mg9[SiO4]4(OH, F)2, a new mineral from Zelentsovskaya mine near Magnitka (Zlatoust district, Southwestern Urals), is the OH-dominant equivalent of clinohumite Mg9[SiO4]4(F,OH)2. The crystal structure of hydroxylclinohumite has been refined from single-crystal X-ray data to R = 0.026 for the 1912 observed unique reflections [Fo > 4σ(Fo): a = 4.7480(3) Å, b = 10.2730(7) Å, c = 13.6894(2) Å, α = 100.72(1)°, V = 656.1(1) Å3, P21/b (No. 14), Z = 2]. Twinning on {001}, which apparently doubles the c axis, was detected and a ratio of 0.94:0.06 between the volumes of the two twin components has been obtained by least-squares refinement. The crystal structure of hydroxylclinohumite corresponds to that of clinohumite except for the positions of the hydrogen atoms. The crystal chemistry of the clinohumite subgroup is discussed and a general formula M2+8(M2+, M4+) (SiO4)4(OH, F, O)2 (M2+ and M4+ mainly Mg and Ti, respectively) is proposed for it.
Zeitschrift für Kristallographie, Oldenbourg Wissenschaftsverlag
Print ISSN: 0044-2968
Volume: 215, 03/2000
Pages: 169