Wiperamingaite, NaCaFe ³⁺ Al(PO ₄ )F ₅ (OH)·H ₂ O, a new mineral from Wiperaminga Hill, South Australia, Australia

Abstract The new mineral wiperamingaite, NaCaFe 3+ Al(PO 4 )F 5 (OH)·H 2 O, was found at the Wiperaminga Hill West Quarry, Boolcoomatta Reserve, Olary Province, South Australia, Australia where it has formed by hydrothermal alteration of triplite–zwieselite. Wiperamingaite occurs in a matrix of quartz, minor triplite and pyrite in association with fluorite, bermanite, leucophosphite and phosphosiderite. Crystals are transparent to translucent, brownish-orange to brownish-pink tablets, up to 0.25 mm across. The mineral has a white streak and vitreous lustre. It is brittle with a splintery fracture. The calculated density is 3.11 g/cm 3 . Optically, the mineral is biaxial (–) with α = 1.538(2), β = 1.599(2), γ = 1.614(2) (white light); 2V = 52(2)°; distinct r > v dispersion; orientation: X = a , Y = b , Z = c ; pleochroism: X colourless, Y brown yellow, Z yellow; Y > Z > X . Electron microprobe analysis provided the empirical formula Na 0.97 Ca 1.01 Fe 3+ 0.92 Al 1.11 (PO 4 ) 0.97 F 4.85 (OH) 1.32 ·0.95H 2 O. Wiperamingaite is orthorhombic, P 2 1 2 1 2 1 , a = 5.3537(11), b = 5.5911(11), c = 26.279(5) Å, V = 786.6(3) Å 3 and Z = 4. The structure of wiperamingaite contains chains of cis-corner connected Feφ 6 octahedra (φ = O, OH and H 2 O) running parallel to [010] decorated with corner-connected PO 4 tetrahedra. Adjacent chains link by corner-connection between the octahedra and tetrahedra to form sheets parallel to the (001) plane. Alφ 6 octahedra (φ = O and F) attach to both sides of the sheets via corner-sharing with PO 4 tetrahedra. Naφ 11 polyhedra share edges and faces to form a layer between the sheets that links to the sheets via Alφ 6 octahedra and Caφ 8 polyhedra.