Crystal structure of low-manganese tinzenite (severginite)

The structure of severginite that corresponds to the low-manganese tinzenite has been refined, and the true distribution of the manganese, iron, and magnesium cations over the structural sites has been found [Syntex P1-bar automated diffractometer MoKα radiation, 5171 reflections with vertical bar Fhkl vertical bar>3σ (Fhkl, Rhkl=0.030]. The unit cell is triclinic a=7.162(2), b=9.207(2), and c=8.972(2) A; α=91.84(2) deg., β=98.16(2) deg., γ=77.34(2) deg.; sp. gr. P1-bar; and Z=1. The results obtained allow one to revise the mineralogical nomenclature that is based on the structural data. The isomorphous ratios and the location of electron on the O(16)-H bond are determined for the new (in composition) member of the axinite group