Clino-suenoite, a newly approved magnesium-iron-manganese amphibole from Valmalenco, Sondrio, Italy

Clino-suenoite, ideally square Mn22+Mg5Si8O22(OH)(2) is a new amphibole of the magnesium-iron-manganese subgroup of the amphibole supergroup. The type specimen was found at the Lower Scerscen Glacier, Valmalenco, Sondrio, Italy, where it occurs in Mn-rich quartzite erratics containing braunite, rhodonite, spessartine, carbonates and various accessory minerals. The empirical formula derived from electron microprobe analysis and single-crystal structure refinement is: Na-A(0.04)B(Mn1.582+Ca0.26Na0.16)(Sigma 2.00)(C)(Mg4.21Mn0.612+Fe0.042+Zn0.01Ni0.01Fe0.083+Al0.04)(Sigma 5.00)(Si8.00O22)-Si-T (W)[(OH1.94F0.06)](Sigma=2.00). Clino-suenoite is biaxial (+), with alpha = 1.632(2), beta = 1.644(2), gamma = 1.664(2) and 2V(meas). = 78(2)degrees and 2V(calc). = 76.3 degrees. The unit-cell parameters in the C2/m space group are a = 9.6128(11), b = 18.073(2), c = 5.3073(6) angstrom, beta= 102.825(2)degrees and V = 899.1(2) angstrom(3) with Z = 2. The strongest ten reflections in the powder X- ray diffraction pattern [d (in angstrom), I, (hkl)] are: 2.728, 100, (151); 2.513, 77, ((2) over bar 02); 3.079, 62, (310); 8.321, 60, (110); 3.421, 54, (131); 2.603, 42, (061); 2.175, 42, (261); 3.253, 41, (240); 2.969, 40, (221); 9.036, 40, (020).