Fluormacraeite, [(H2O)K]Mn2(Fe2Ti)(PO4)4[OF](H2O)10 ⋅ 4H2O, the first type mineral from the Plößberg pegmatite, Upper Palatinate, Bavaria, Germany

Fluormacraeite, [(H2O)K]Mn-2(Fe2Ti)(PO4)(4)[OF](H2O)(10) & sdot; 4H(2)O, is a new monoclinic member of the paulkerrite group from the Pl & ouml;ss berg pegmatite, Upper Palatinate, Bavaria, Germany. It was found in specimens of magnesium-bearing triplite. Associated minerals are spherical blue phosphosiderite, pink-coloured strengite micro-crystals, white fluorapatite globules, light-yellow leucophosphite, black-green rockbridgeite, and reddish-brown cacoxenite. Fluormacraeite occurs as isolated pale-yellow rhombic tablets, flattened on (010) with diameters in the range of 50 to 150 mu m and thicknesses on the order of 10 to 30 mu m. The crystal forms are {010}, {001}, and {111}. The calculated density for the empirical formula and single-crystal unit-cell volume is 2.39 g cm(-3). Optically, fluormacraeite crystals are biaxial (+), with alpha=1.610(3), beta=1.620(3), and gamma=1.644(3) (measured in white light). The calculated 2V is 66.5 degrees. The optical orientation is X=b, Y=c, and Z=a. The empirical formula from electron microprobe analyses and structure refinement is (A1)[K-0.14(H2O)(0.76)](Sigma 0.90) (A2)[K-0.79(H2O)(0.21)](Sigma 1.00) (M1)(MnMg0.25)(Sigma 2.00) (M2+M3)(FeAl0.13TiMg0.01)(Sigma 3.00) (PO4)(4.00) (X)[O0.94F0.81(OH)(0.25)](Sigma 2.00)(H2O)(10) & sdot; 3.90H(2)O. Fluormacraeite has monoclinic symmetry with space group P2(1)/c and unit-cell parameters a=10.546(2) & Aring;, b=20.655(1) & Aring;, c=12.405(1) & Aring;, beta=90.09(1)degrees, V=2702.1(6) & Aring;(3), and Z=4. The crystal structure was refined using synchrotron single-crystal data to wR(obs)=0.0559 for 5646 reflections with I>3 sigma(I). Fluormacraeite is isostructural with the paulkerrite-group minerals pleysteinite, macraeite, rewitzerite, hochleitnerite, fluor-rewitzerite, sperlingite, and paulkerrite, with ordering of K and H2O at different A sites (A1 and A2) using the general formula A1A2M1(2)M2(2)M3(PO4)(4)X-2(H2O)(10) & sdot; 4H(2)O. It is the F analogue of macraeite, with OF replacing O(OH) at the X2 sites. The general crystal-chemical properties of the monoclinic paulkerrite-group minerals are compared.