Pleysteinite, [(H₂O)_0.5K_0.5]₂Mn₂Al₃(PO₄)₄F₂(H₂O)₁₀ ⋅ 4H₂O, the Al analogue of benyacarite, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany

Abstract. Pleysteinite, [(H2O)0.5K0.5]2Mn2Al3(PO4)4F2(H2O)10 ⚫ 4H2O, is the aluminium analogue of benyacarite, from Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in specimens altered zwieselite, association with nordgauite, fluellite, rockbridgeite, pyrite and columbite. Pleysteinite occurs as isolated small aggregates colourless, stubby prisms that are typically 10 to 30 µm wide up 100 long. The crystals flattened on {010} bounded by {111}, {100} {001} planes. calculated density 2.34 g cm−3. Optically, pleysteinite biaxial (+), α=1.566(2), β=1.580(2), γ=1.600(2) (measured white light) 2V(meas.) = 80(1)∘. empirical formula electron microprobe analyses structure refinement [(H2O)0.50K0.50]2(Mn1.20Mg0.49Fe0.272+Zn0.05)∑2.01(Al1.63Fe0.203+Ti0.194+)∑2.02(Al0.56Ti0.444+) (PO4)4.02[F0.58O0.31(OH)0.11]2(H2O)10 3.92H2O. has orthorhombic symmetry, space group Pbca unit-cell parameters a 10.4133(8) Å, b=20.5242(17) c=12.2651(13) V=2621.4(4) Å3 Z=4. crystal refined using single-crystal data wRobs=0.054 for 1692 reflections I>3σ(I). contains corner-connected linear trimers Al-centred octahedra share corners PO4 tetrahedra form 10-member rings parallel (010). K+ cations water molecules located rings. Additional corner-sharing Mn(H2O)4O2 along [010] complete 3D framework structure.