Wangkuirenite—a new lead chloride-selenite mineral
A new mineral species,wangkuirenite,ideally Pb3Cl2(Se4+O3)2,was discovered from the old lead-arsenic mine of Baccu Locci,Sardinia,Italy.It occurs as tabular or bladed crystals.Associated minerals include chalcomenite,orlandiite,olsacherite,anglesite,and quartz.Wangkuirenite is very pale yellow in transmitted light,transparent with a white streak and vitreous luster.It is brittle and has a Mohs hardness of～3.Cleavage is perfect on(001).No twinning or parting was observed.The calculated density is 6.48 g/cm3.An electron microprobe analysis yielded an empirical formula[based on 8(O+Cl)apfu]Pb3.01Cl1.96(Se1.00O3.02)2.Wangkuirenite is the natural counterpart of synthetic Pb3Cl2(SeO3)2 and isostructural with synthetic Pb3Br2(SeO3)2 and Pb3I2(SeO3)2.It is monoclinic with space group C2/c and unit-cell parameters a=13.4266(4),b=5.5826(2),c=13.0024(4)Å,β=94.287(2)°,V=971.87(5)Å3,and Z=4.The crystal structure of wangkuirenite is characterized by Pb2+-(Se4+O3)2-layers parallel to(001),which are interconnected by Cl-anions.There are two distinct Pb2+cations(Pb1 and Pb2),one(Se4+O3)2-anionic group,and one Cl-anion in an asymmetric unit.The Se4+cation is bonded to three O atoms,forming a typical(Se4+O3)2-trigonal pyramid.Both Pb1 and Pb2 are 8-coordinated,with Pb1 surrounded by(2Cl+6O)and Pb2 by(3Cl+5O).The O and Cl anions are distributed around both Pbl and Pb2,suggesting that their 6s2 lone-pair electrons are inert.Wangkuirenite is one of six lead-chloride-selenite minerals documented thus far and it is closely related both structurally and chemically to sarrabusite,Pb5CuC14(SeO3)4.
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