Crystal structure refinement of aluminian lizardite-2H2

Well-crystallized euhedral crystals of aluminian lizardite-2H2 (Mg2.35Fe2+ 0.06Fe3+ 0.07Al0.52) (Si1.41Al0.59)O5.00(OH)4.00 were found near Schio (Vicenza, Italy). To gain insight into the role of a high Al content lizardite, chemical analyses and single-crystal X-ray data collection were conducted. Structure refinement, completed in space group P63 (agreement factor R = 0.034), gives mean T-O values of 1-654 Å and 1.664 Å for T1 and T2 sites, respectively. The ditrigonal distortion of the six-membered tetrahedral ring is positive (? = +9.7°), as expected for the 2H2 polytype. The octahedral site has a mean bond length similar to that of the Mg-rich octahedra of amesite and distortion parameters similar to those of Al-rich octahedra.