Bergbauerite, (H ₂ O) ₂ Mn ²⁺ 2(Fe ₂ Ti)(PO ₄ ) ₄ [(OH) ₂ [(H ₂ O) ₁₀ ]·4H ₂ O, from the Hühnerkobel pegmatite, Bavaria, and revised nomencl

Bergbauerite, (H 2 O) 2 Mn 2+ 2 (Fe 2 Ti)(PO 4 ) 4 [(OH) 2 [(H 2 O) 10 ]4H 2 O, is a new orthorhombic member of the paulkerrite group, from the Hhnerkobel pegmatite, Bavaria, Germany.It occurs in solution cavities in altered zwieselite, in association with fluorapatite, leucophosphite, jahnsite-(CaMnFe), whiteite-(CaMnFe), phosphosiderite, ferrostrunzite, manganese oxides and other members of the paulkerrite mineral group.Bergbauerite forms isolated and intergrown colourless rhombic tablets, up to 150 m.The tablets are flattened on {010} and show the forms {010}, {111} and {11-1}.The calculated density is 2.38 g cm -3 .Optically, bergbauerite crystals are biaxial (+) with = 1.635(3), = 1.645(3), = 1.657(3) (white light) and 2V (calc.)= 85.4.The empirical formula in structural form is A [K 0.23 (H 2 O) 1.77 ] 2.00 M1 (Mn 2+ 0.96 Mg 0.24 Fe 3+ 0.82 ) 2.02 M2+M3 (Fe 3+ 1.60 Ti 4+ 1.43 ) 3.03 (PO 4 ) 3.95 X [(OH) 1.07 O 0.93 ] 2.00 [(H 2 O) 9.18 (OH) 0.82 ] 3.91H 2 O. Bergbauerite has orthorhombic symmetry with space group Pbca and unit-cell parameters a = 10.547(2),b = 20.406(4),c = 12.478(2), V = 2684.5(8) 3 and Z = 4.The crystal structure was refined using synchrotron singlecrystal data to R obs = 0.058 for 2560 reflections with I > 3(I).A proposal to modify the nomenclature for the paulkerrite group minerals to allow new root names to be applied to group members that have different dominant species at the A and M sites has been approved.