ABSTRACT
The crystal structure of zharchikhite, AlF(OH)2, from the Zharchikhinskoe deposit (Buryatia, Russia) is solved here using single-crystal X-ray diffraction. The mineral is monoclinic, space group P21/c, a = 5.1788â (4), b = 7.8386â (4), c = 5.1624â (4)â Å, ß = 116.276â (10)°, V = 187.91â (3)â Å3 and Z = 4. Zharchikhite demonstrates a novel structure type roughly related to the α-PbO2 structure type and different from other compounds of the Al-F-OH system. The crystal structure of zharchikhite is based on the octahedral pseudoframework built from zigzag chains of edge-sharing AlF2(OH)4 octahedra; adjacent chains are linked via F vertices and the pseudoframework contains wide channels.
ABSTRACT
The crystal chemistry of the natural microporous two-layer aluminosilicates (2D zeolites) latiumite and tuscanite is re-investigated based on new data on the chemical composition, crystal structures, and infrared and Raman spectra. The CO32--depleted and P- and H-enriched samples from Sacrofano paleovolcano, Lazio, Italy, are studied. Both minerals are monoclinic; latiumite P21, a = 12.0206â (3), b = 5.09502â (10), c = 10.8527â (3)â Å, ß = 107.010â (3)°, V = 635.60â (3)â Å3 and tuscanite P21/a, a = 23.9846â (9), b = 5.09694â (15), c = 10.8504â (4)â Å, ß = 107.032â (4)°, V = 1268.26â (8)â Å3. The obtained crystal chemical formulae (Z = 2 for both minerals) are [(H3O)0.48(H2O)0.24K0.28](Ca2.48K0.21Na0.21Sr0.06Mg0.04)(Si2.86Al2.14O11)[(SO4)0.70(PO4)0.20](CO3)0.10 for latiumite and [(H3O)0.96(H2O)0.58K0.46](Ca4.94K0.44Na0.45Sr0.09Mg0.08)(Si5.80Al4.20O22)[(SO4)1.53(PO4)0.33](CO3)0.14 for tuscanite. These minerals are dimorphous. Both latiumite and tuscanite show distinct affinity for the PO43- anion. Hydrolytic alteration of these minerals results in partial leaching of potassium accompanied by protonation and hydration which is an important precondition for the existence of ion/proton conductivity of related materials.
