Bederite, ideally []Ca 2 Mn (super 2+) 2 Fe (super 3+) 2 Mn (super 2+) 2 (PO 4 ) 6 (H 2 O) 2 , orthorhombic, a = 12.559(2), b = 12.834(1), c = 11.714(2) Aa, V = 1887.8(4) Aa 3 , Z = 4, space group Pcab, is a new mineral from the El Penon pegmatite, Nevados de Palermo, Salta Province, Republica Argentina. The mineral occurs as rare ellipsoidal nodules (approximately 5 cm in diameter) enclosed in potassium feldspar or quartz at the core-margin zone of a beryl-type rare-element pegmatite. Associated minerals are quartz, potassium feldspar, muscovite, beryl, columbite, possibly heterosite, and powdery coatings of Mn- and Fe-oxides; in the dumps of the pegmatite, there are numerous other phosphates including altered triphylite-lithophyllite, arrojadite, eosphorite, laueite, brazilianite, and fairfieldite. Bederite is very dark brown to black with a dark olive-green streak and a vitreous luster. It is brittle with an irregular fracture and a good cleavage parallel to {100}, Mohs hardness is 5, and the observed and calculated densities are 3.48(1) and 3.50 g/cm 3 , respectively. In transmitted plane-polarized light, bederite is pleochroic X = Y = olive green, Z = brown with X = Y>Z and X = a, Y = c, Z = b. In cross-polarized light, it is biaxial negative with strong dispersion, v>r, 2V(obs) = 54 degrees and 2V(calc) = 60 degrees . Refractive indices are as follows: alpha = 1.729(3), beta = 1.738(3), gamma = 1.741(3). Chemical analysis by electron microprobe plus the Penfield method and thermogravimetry gave P 2 O 5 41.76, Al 2 O 3 0.82, Fe 2 O 3 12.00, FeO 2.25, MnO 20.59, MgO 3.45, ZnO 0.40, CaO 10.91, SrO 0.43, Na 2 O 0.63, H 2 O 3.52, sum 96.76 wt% where the Fe 2 O 3 and FeO contents were derived from the refined crystal structure. The five strongest lines in the X-ray powder diffraction pattern are as follows: d (Aa), I, (h k l): 2.768, 100, (4 0 2); 2.927, 78, (0 0 4); 3.006, 67, (1 4 1); 2.814, 35, (0 4 2); 2.110, 33, (1 6 0). The crystal structure of bederite was refined to an R index of 2.8% based on 2530 observed (>5sigma F) reflections measured with MoKalpha X-radiation. Bederite is isostructural with wicksite, grischunite, and an unnamed wicksite-like phase; it is related to wicksite by the substitutions Na [] + M2 Fe (super 3+) --> Na Na + M2Mg, M1 Mn (super 2+) --> M1 Fe (super 2+) and M3 Mn (super 2+) --> M3 Fe (super 2+) .

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