Hochleitnerite, [K(H₂O)]Mn₂(Ti₂Fe)(PO₄)₄O₂(H₂O)₁₀  ⋅  4H₂O, a new paulkerrite-group mineral, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany

Abstract

Hochleitnerite, [K(H2O)]Mn2(Ti2Fe)(PO4)4O2(H2O)10 ⋅ 4H2O, is a new paulkerrite-group mineral from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in specimens of altered zwieselite, in association with fluorapatite, rockbridgeite, columbite and sub-micrometre rods of uranophane. Hochleitnerite occurs as isolated and intergrown pale-yellow, diamond-shaped tablets with thicknesses reaching 50 µm and lengths of 120 µm. The crystals are flattened on {010}, slightly elongated on [001], and bounded by the {111} and {010} forms. The calculated density is 2.40 g cm−3. Optically, hochleitnerite crystals are biaxial (+), with α= 1.615(2), β= 1.621(2) and γ= 1.645(2) (measured in white light). The calculated 2V is 53.8∘. The empirical formula is [K(H2O)](Mn1.512+Fe0.492+)Σ2.00(Ti1.624+Fe0.193+Al0.15)Σ2.96(PO4)4.00[O1.50F0.23(OH)0.27]Σ2.00(H2O)10 ⋅ 4H2O. Hochleitnerite has space group Pbca and unit-cell parameters a= 10.5513(3) Å, b= 20.6855(17) Å, c= 12.4575(4) Å, V= 2718.96(15) Å3 and Z= 4. The crystal structure was refined using single-crystal data to wRobs= 0.082 for 2242 reflections with I > 3σ(I). The crystal structure contains corner-connected linear trimers of Ti-centred octahedra that share corners with PO4 tetrahedra to form 10-member rings parallel to (010). K+ cations and water molecules are located within the rings. Additional corner sharing of the PO4 tetrahedra with MnO2(H2O)4 octahedra occurs along [010] to complete the 3D framework structure.