Bohuslavite, Fe 4 3 + (PO4)3(SO4)(OH)(H2O)10·nH2O, a new hydrated iron phosphate-sulfate

The new mineral species bohuslavite, Fe 4 3 + (PO4)3(SO4)(OH)(H2O)10·nH2O (5 = n = 14), has been discovered in the Buca della Vena baryte ± iron oxides ± pyrite ore deposit, Apuan Alps, Tuscany (Italy), and in the Horní Mesto deposit, northern Moravia (Czech Republic). It occurs as pinkish to lilac tabular {001} crystals, with a pseudohexagonal outline, up to 0.25 mm in size, forming globular aggregates up to 1 mm across. At both localities, it is associated with gypsum. Optically, bohuslavite is biaxial negative. Indices of refraction and 2V angles, measured with white light, are a = 1.537(2), ß = 1.567(1), ? = 1.568(1), 2V = 16(3)° and a = 1.550(2), ß = 1.579(2), ? = 1.579(1), 2V = 5–10° for the samples from Buca della Vena (BdV) and Horní Mesto (HM), respectively. Dispersion, with r > v, is slight in BdV sample and it was not observed in HM. In both cases, X ˜ c. No pleochroism was observed. Electron microprobe analyses gave (in wt% – mean of 10 spot analyses on each sample): SO3 10.92, P2O5 25.34, Al2O3 0.26, Fe2O3 40.70, H2O 35.96, total 113.18 (BdV), and SO3 9.32, P2O5 24.84, Al2O3 0.30, Fe2O3 36.63, H2O 32.49, total 103.58 (HM). The H2O contents were determined through thermo-gravimetric analyses. Mössbauer spectroscopy indicated that all iron occurs as Fe3+. Thus, the empirical formulae of bohuslavite, based on S(Fe,Al) = 4 atoms per formula unit (apfu), are (Fe3.96Al0.04)(PO4)2.77(SO4)1.06(OH)1.56(H2O)10·7.90H2O (BdV) and (Fe3.95Al0.05)(PO4)3.02(SO4)1.00(OH)0.94(H2O)10·5.08H2O (HM), ideally Fe 4 3 + (PO4)3(SO4)(OH)(H2O)10·nH2O. Bohuslavite is triclinic, space group P 1 ¯ , with a = 13.376(3), b = 13.338(3), c = 10.863(4) Å, a = 92.80(2), ß = 91.03(2), ? = 119.92(2)°, V = 1675.7(9) Å3, Z = 2 (sample BdV). The crystal structure was solved and refined to R 1 = 0.232 on the basis of 2177 unique reflections with F o > 4s (F o) and 208 refined parameters. Its crystal structure is based on {001} heteropolyhedral layers with composition [Fe4(PO4)3O(OH)(H2O)10]. These layers are decorated, on both sides, by SO4 groups. Additional H2O groups are hosted in the interlayers and in the [001] channels. The name bohuslavite honours the Czech mineralogist and geologist Bohuslav Fojt for his contributions to mineralogy and economic geology. A third occurrence of bohuslavite from the Jeremias Glück mine, Garnsdorf near Saalfeld, Thuringia (Germany), is briefly discussed.