Manganoblödite, Na2Mn(SO4)2·4H2O, and cobaltoblödite, Na2Co(SO4)2·4H2O: two new members of the blödite group from the Blue Lizard mine, San Juan County, Utah, USA

Two new minerals – manganoblodite (IMA2012–029), ideally Na 2 Mn(SO 4 ) 2 ·4H 2 O, and cobaltoblodite (IMA2012–059), ideally Na 2 Co(SO 4 ) 2 ·4H 2 O, the Mn-dominant and Co-dominant analogues of blodite, respectively, were found at the Blue Lizard mine, San Juan County, Utah, USA. They are closely associated with blodite (Mn-Co-Ni-bearing), chalcanthite, gypsum, sideronatrite, johannite, quartz and feldspar. Both new minerals occur as aggregates of anhedral grains up to 60 μm (manganoblodite) and 200 μm (cobaltoblodite) forming thin crusts covering areas up to 2×2 cm on the surface of other sulfates. Both new species often occur as intimate intergrowths with each other and also with Mn-Co-Ni-bearing blodite. Manganoblodite and cobaltoblodite are transparent, colourless in single grains and reddish-pink in aggregates and crusts, with a white streak and vitreous lustre. Their Mohs9 hardness is ~2½. They are brittle, have uneven fracture and no obvious parting or cleavage. The measured and calculated densities are D meas = 2.25(2) g cm −3 and D calc = 2.338 g cm −3 for manganoblodite and D meas = 2.29(2) g cm −3 and D calc = 2.347 g cm −3 for cobaltoblodite. Optically both species are biaxial negative. The mean refractive indices are α = 1.493(2), β = 1.498(2) and γ = 1.501(2) for manganoblodite and α = 1.498(2), β = 1.503(2) and γ = 1.505(2) for cobaltoblodite. The chemical composition of manganoblodite (wt.%, electron-microprobe data) is: Na 2 O 16.94, MgO 3.29, MnO 8.80, CoO 2.96, NiO 1.34, SO 3 45.39, H 2 O (calc.) 20.14, total 98.86. The empirical formula, calculated on the basis of 12 O a.p.f.u., is: Na 1.96 (Mn 0.44 Mg 0.29 Co 0.14 Ni 0.06 ) Σ0.93 S 2.03 O 8 ·4H 2 O. The chemical composition of cobaltoblodite (wt.%, electron-microprobe data) is: Na 2 O 17.00, MgO 3.42, MnO 3.38, CoO 7.52, NiO 2.53, SO 3 45.41, H 2 O (calc.) 20.20, total 99.46. The empirical formula, calculated on the basis of 12 O a.p.f.u., is: Na 1.96 (Co 0.36 Mg 0.30 Mn 0.17 Ni 0.12 ) Σ0.95 S 2.02 O 8 ·4H 2 O. Both minerals are monoclinic, space group P 2 1 / a , with a = 11.137(2), b = 8.279(1), c = 5.5381(9) A, β = 100.42(1)°, V = 502.20(14) A 3 and Z = 2 (manganoblodite); and a = 11.147(1), b = 8.268(1), c = 5.5396(7) A, β = 100.517(11)°, V = 501.97(10) A 3 and Z = 2 (cobaltoblodite). The strongest diffractions from X-ray powder pattern [listed as ( d , A( I )( hkl )] are for manganoblodite: 4.556(70)(210, 011); 4.266(45)(2I01); 3.791(26)(2I11); 3.338(21)(310); 3.291(100)(220, 021), 3.256(67)(211, 1I21), 2.968(22)(2I 21), 2.647(24)(4I01); for cobaltoblodite: 4.551(80)(210, 011); 4.269(50)(2I01); 3.795(18)(2I11); 3.339(43)(310); 3.29(100)(220, 021), 3.258(58)(211, 1I21), 2.644(21)(4I01), 2.296(22)(1I22). The crystal structures of both minerals were refined by single-crystal X-ray diffraction to R 1 = 0.0459 (manganoblodite) and R 1 = 0.0339 (cobaltoblodite).