王奎仁石:一种铅的氯化物-亚硒酸盐新矿物

Wangkuirenite—a new lead chloride-selenite mineral

王奎仁石(wangkuirenite),理想式Pb_(3)Cl_(2)(Se^(4+)O_(3))_(2),发现于意大利撒丁岛巴库鲁奇(Baccy Rucci)铅-砷老矿山。该新矿物以板状或叶片状晶体产出,与其共生的矿物有蓝硒铜矿、沃兰迪石、硒铅矾、铅矾和石英。王奎仁石在透射光下为很淡的黄色,晶体透明、具玻璃光泽,条痕为白色,性脆,其摩氏硬度约为3。沿(001)面的解理完全,未观察到有双晶或裂理。计算密度为6.48 g/cm^(3)。根据电子探针分析结果和基于每个单元中有8个(O+Cl)原子获得王奎仁石的经验化学式为Pb_(3.01)Cl_(1.96)(Se_(1.00)O_(3.02))_(2)。王奎仁石是与人工合成Pb_(3)Cl_(2)(SeO_(3))_(2)相对应的天然矿物,与人工合成的Pb_(3)Br_(2)(SeO_(3))_(2)和Pb_(3)I_(2)(SeO_(3))_(2)具有相同的晶体结构。王奎仁石属单斜晶系,空间群为C2/c,晶胞参数为a=13.4266(4),b=5.5826(2),c=13.0024(4)Å,β=94.287(2)º,V=971.87(5)Å3,Z=4。王奎仁石晶体结构的特点具有平行于(001)面的Pb^(2+)-(Se^(4+)O_(3))_(2)–结构层,层间靠阴离子Cl−相互连结起来。结构中一个非对称的单元内,存在有两种不同位置的Pb^(2+)阳离子(Pb_(1)和Pb_(2))、一个(Se^(4+)O_(3))_(2)−阴离子团和一个Cl−阴离子。该Se^(4+)阳离子与3个O原子相结合,形成(Se^(4+)O_(3))_(2)−三次配位。两个Pb_(1)和Pb_(2)均为8次配位,分别为[PbCl_(2)O_(6)]和[PbCl_(3)O_(5)],阴离子O和Cl围绕Pb_(1)和Pb_(2)的分布表明,它们的6s2孤对电子是惰性的。王奎仁石是迄今记录到的6个铅的氯化物-亚硒酸盐矿物中的一个成员,在结构和成分上它与萨拉巴斯石[sarrabusite,Pb_(5)CuCl_(4)(SeO_(3))_(4)]紧密相关。

A new mineral species,wangkuirenite,ideally Pb_(3)Cl_(2)(Se^(4+)O_(3))_(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/cm^(3).An electron microprobe analysis yielded an empirical formula[based on 8(O+Cl)apfu]Pb_(3.01)Cl_(1.96)(Se_(1.00)O_(3.02))_(2).Wangkuirenite is the natural counterpart of synthetic Pb_(3)Cl_(2)(SeO_(3))_(2) and isostructural with synthetic Pb_(3)Br_(2)(SeO_(3))_(2) and Pb_(3)I_(2)(SeO_(3))_(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)º,V=971.87(5)Å3,and Z=4.The crystal structure of wangkuirenite is characterized by Pb^(2+)-(Se^(4+)O_(3))_(2)−layers parallel to(001),which are interconnected by Cl−anions.There are two distinct Pb^(2+)cations(Pb_(1) and Pb_(2)),one(Se^(4+)O_(3))_(2)−anionic group,and one Cl−anion in an asymmetric unit.The Se^(4+)cation is bonded to three O atoms,forming a typical(Se^(4+)O_(3))_(2)−trigonal pyramid.Both Pb_(1) and Pb_(2) are 8-coordinated,with Pb_(1) surrounded by(2Cl+6O)and Pb_(2) by(3Cl+5O).The O and Cl anions are distributed around both Pb_(1) and Pb_(2),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,Pb_(5)CuCl_(4)(SeO_(3))_(4).