Parascorodite, FeAsO4 center dot 2H(2)O - a new mineral from Kank near Kutna Hora, Czech Republic

Parascorodite, a new mineral from Kank near Kutna Hora, Central Bohemia, Cz ech 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, Fe2 O3 34.55, Al2O3 0.17, H2O 17.81, totaling 99.95. The simplified chemical fo rmula is FeAsO4. 2H(2)O. Selected area electron diffraction suggests hexago nal or trigonal symmetry. The extinction symbol is P-c-. Powder X-ray diffr action yielded unit-cell parameters a = 8.9327(5) Angstrom, c = 9.9391(8) A ngstrom, V = 686.83(8) Angstrom(3), Z = 6. Densities (measured and calculat ed, respectively) are D-m = 3.213(3) g/cm(3) and D-x = 3.212 g/cm(3). SEM a nd TEM images showed that basal sections of parascorodite are hexagonal in shape; thicker prismatic crystals were also observed. Crystal size varies b etween 0.1 to 0.5 mu m. 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 si ze, (n) over bar (calc) = 1.797. The TG curve shows two weight losses. at 2 0-150 degrees C (2.1 wt%, absorbed water) and at 150-620 degrees C (15.5 wt %, molecular water), respectively. They correspond to the endothermic peaks on the DTA curve at 120 and 260 degrees C. Strong exothermic reaction obse rved at 585 degrees C reflects formation of the phase FeAsO4. Infrared abso rption spectra of parascorodite are close to those of scorodite.