• journal_title：The Canadian Mineralogist
• Contributor：Frank C. Hawthorne ; Yassir A. Abdu ; Kimberly T. Tait ; Malcolm E. Back
• Publisher：Mineralogical Association of Canada
• Date：2013-04-01
• Format：text/html
• Language：en
• Identifier：10.3749/canmin.51.2.243
• journal_abbrev：Can Mineral
• issn：0008-4476
• volume：51
• issue：2
• firstpage：243
• section：Articles

The crystal structure of yofortierite, (Mn²⁺,Mg,Fe³⁺,□)₅Si₈O₂₀(OH,H₂O)₂(H₂O)₇, monoclinic, C2/m, Z = 4, a 14.1686(12), b 17.8583(16), c 5.2919(5) Å, β 105.878(1)°, V 1287.9(3) ų, has been refined to R₁ = 4.9 % for 1795 unique (F_o > 4σF) reflections collected on a Bruker D8 three-circle diffractometer equipped with a rotating-anode generator (MoKα X-radiation), a multi-layer optics incident-beam path, and an APEX-II CCD detector. Chemical analysis by electron microprobe plus Fe³⁺ determination by Mössbauer spectroscopy gave SiO₂ 51.78, Al₂O₃ 0.05, TiO₂ 0.15, Fe₂O₃ 1.84, MnO 22.97, ZnO 0.99, MgO 4.32, CaO 1.10, H₂O_calc 16.69, sum 99.89 wt.%. The resulting empirical formula is (Mn_3.01Mg_1.00Zn_0.11Ca_0.18Fe³⁺_0.21 Ti_0.02Al_0.01□_0.46) _∑=5Si_8.00O₂₀[(OH)_1.34(H₂O)_0.66]_∑=2(H₂O)₇. Yofortierite is a palygorskyite-group mineral. There are two tetrahedrally coordinated T sites occupied by Si with <Si–O> distances of 1.621 and 1.617 Å, and three octahedrally coordinated M sites, occupied primarily by Mn²⁺ and Mg with minor Fe³⁺ and □, with <M–O> distances of 2.147, 2.079, and 2.183 Å. The <M–O> distances indicate strong order of M cations over the three M sites, with the smaller cations and vacancies ordered at the M(2) site and Ca ordered at the M(3) site. The presence of vacancies at the M(2) site locally couple with the replacement of (OH)⁻ at the O(4) site by (H₂O)^o, giving rise to strong short-range order, and H₂O is incorporated into the framework part of the structure by the substitution Mn²⁺ + (OH)⁻ = □ + (H₂O)^o which is coupled to the substitution Mn²⁺ = Fe³⁺ by the requirement of electroneutrality.