Lead-antimony sulfosalts from Tuscany (Italy). X. Dadsonite from the Buca delta Vena mine and Bi-rich izoklakeite from the Seravezza marble quarries

Two very rare Pb sulfosalts, dadsonite and izoklakeite, discovered in the Apuan Alps, represent the first Italian occurrence and were characterized by electron probe microanalysis and X-ray diffraction. Dadsonite from the Buca della Vena Ba-Fe deposit (two samples) has formula and Pb22.64Sb24.90S60Cl1.12 and (Pb22.90Cu0.01)Sb25.12S60Cl1.07, in fair agreement with the ideal formula Pb23Sb25S60Cl.. XRPD gives the monoclinic unit cell a 19.058(3), b 8.234(2), c 17.352(3) angstrom, beta 96.33(2)degrees. Dadsdnite, with both pillaite and pellouxite, is the third chloro-sulfosalt from Buca della Vena, that reveals a high chlorinity of mineralizing solutions. Izoklakeite from Seravezza has the mean composition (wt.%) Pb 45.69, Bi 24.89, Sb 8.16, Cu 1.08, Ag 0.74, Hg 0.29, S 15.43, Se 2.86, sum 99.14, with structural formula Cu-1.92[Ag0.77Hg0.16Pb24.49(Bi13.23Sb7.44)(Sigma=20.67)](Sigma=46.09)(S-53.43 Se-4.02)(Sigma-57.45). It is a Bi-rich izoklakeite, close to the ideal Fe- and Ag-free formula, Cu2Pb26(Bi,Sb)(20)S-57. Significant Se and Hg contents constitute chemical peculiarities of this occurrence. XRPD gives the orthorhombic unit cell a 34.272(4), b 38.351(5), c 4.098(1) angstrom.