Parascorodite FeAsO4 2H2O, a new mineral from Kank near Kutna Hora, Czech Republic

Parascorodite, a new mineral from Kank near Kutna Hora, Central Bohemia, Czech Republic, forms earthy white to white-yellow aggregates associated with scorodite, pitticite, bukovskyite, kankite, zykaite, gypsum, and jarosite, wet chemical analysis gave (in wt%): As2O5 44.45, P2O5 0.84, SO3 1.53, Fe2O3 34.55, Al2O3 0.17, H2O 17.81, totaling 99.95. The simplified chemical formula is FeAsO4·2H2O. Selected area electron diffraction suggests hexagonal or trigonal symmetry. The extinction symbol is P-c-. Powder X-ray diffraction yielded unit-cell parameters a = 8.9327(5) Å, c = 9.9391(8) Å, V = 686.83 (8) Å3, Z = 6. Densities (measured and calculated, respectively) are D(m) = 3.213(3) g/cm3 and D(x) = 3.212 g/cm3. SEM and TEM images showed that basal sections of parascorodite are hexagonal in shape; thicker prismatic crystals were also observed. Crystal size varies between 0.1 to 0.5 μm. The strongest lines in the X-ray powder diffraction pattern are [d[I](hkl)]: 4.184(44)(012), 4.076(100)(111), 3.053(67)(202), 2.806(68)(211), 2.661(59)(113), 2.520(54)(212), 2.2891(44)(032). Refractive indexes could not have been measured due to extremely small crystallite size, n̄ (calc) = 1.797. The TG curve shows two weight losses: at 20-150 °C (2.1 wt%, absorbed water) and at 150-620 °C (15.5 wt%, molecular water), respectively. They correspond to the endothermic peaks on the DTA curve at 120 and 260 °C. Strong exothermic reaction observed at 585 °C reflects formation of the phase FeAsO4. Infrared absorption spectra of parascorodite are close to those of scorodite.