Sperlingite, (H₂O)K(Mn²⁺Fe³⁺)(Al₂Ti)(PO₄)₄[O(OH)][(H₂O)₉(OH)]⋅4H₂O, a new paulkerrite-group mineral, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany.

Sperlingite, (H 2 O)K(Mn 2+ Fe 3+ )(Al 2 Ti)(PO 4 ) 4 [O(OH)][(H 2 O) 9 (OH)]⋅4H 2 O, is a new monoclinic member of the paulkerrite group, from the Hagendorf-Süd pegmatite, Oberpfalz, Bavaria, Germany. It was found in corrosion pits of altered zwieselite, in association with columbite, hopeite, leucophosphite, mitridatite, scholzite, orange–brown zincoberaunite sprays and tiny green crystals of zincolibethenite. Sperlingite forms colourless prisms with pyramidal terminations, which are predominantly only 5 to 20 μm in size, rarely to 60 μm and frequently are multiply intergrown and are overgrown with smaller crystals. The crystals are flattened on {010} and slightly elongated along [100] with forms {010}, {001} and {111}. Twinning occurs by rotation about c . The calculated density is 2.40 g⋅cm –3 . Optically, sperlingite crystals are biaxial (+), α = 1.600(est), β = 1.615(5), γ = 1.635(5) (white light) and 2V (calc.) = 82.7°. The optical orientation is X = b , Y = c and Z = a . Neither dispersion nor pleochroism were observed. The empirical formula from electron microprobe analyses and structure refinement is A 1 [(H 2 O) 0.96 K 0.04 ] Σ1.00 A 2 (K 0.52 □ 0.48 ) Σ1.00 M 1 (Mn 2+ 0.60 Mg 0.33 Zn 0.29 Fe 3+ 0.77 ) Σ1.99 M 2 +M 3 (Al 1.05 Ti 4+ 1.33 Fe 3+ 0.62 ) Σ3.00 (PO 4 ) 4 X [F 0.19 (OH) 0.94 O 0.87 ] Σ2.00 [(H 2 O) 9.23 (OH) 0.77 ] Σ10.00 ⋅3.96H 2 O. Sperlingite has monoclinic symmetry with space group P 2 1 / c and unit-cell parameters a = 10.428(2) Å, b = 20.281(4) Å, c = 12.223(2) Å, β = 90.10(3)°, V = 2585.0(8) Å 3 and Z = 4. The crystal structure was refined using synchrotron single-crystal data to wR obs = 0.058 for 5608 reflections with I > 3σ( I ). Sperlingite is the first paulkerrite-group mineral to have co-dominant divalent and trivalent cations at the M 1 sites; All other reported members have Mn 2+ or Mg dominant at M 1. Local charge balance for Fe 3+ at M 1 is achieved by H 2 O → OH – at H 2 O coordinated to M 1.