我国首次发现的天然硅铋石的矿物学研究

Mineralogical studies of eulytite found for the first time in China

硅铋石是一种极为罕见的铋的硅酸盐矿物,本次报道的天然硅铋石产于我国内蒙古自治区东乌旗朝不楞矽卡岩型铁多金属矿床中,附生在蔷薇辉石晶洞或裂隙中的透闪石纤维上.常见四面体{111}及三角三四面体晶形,一般粒径为0.07～0.15 mm,颜色多为浅黄色,透明,玻璃光泽,性脆,条痕为无色,维氏硬度VHN（100g）=487～583kg/mm2,平均535 kg/mm2,摩氏硬度5,计算密度7.11 g/cm3,计算折射率N=2.15.矿物化学分子式为Bi4Si3O12.X射线衍射强线[d（（A））（I）]为4.26 （85）、3.29 （100）、2.77（79）、2.11（45）和1.67（33）,结构精修晶胞参数a＝10.116（2）（A）,V=1 035.2（7）（A）3,空间群为I-43d,Z=4.本文还对硅铋石的成因进行了初步探讨.

Eulytite is an extremely rare bismuth silicate mineral.The natural eulytite reported in this paper is attached on the geodes or cracks of tremoilite fibers produced in the Chaobuleng skarn-type iron-polymetallic deposit in Dong Ujimqin Banner of Inner Mongolia.The eulytite commonly has the forms of tetrahedron {111} and trigonal tristetrahedron,crystal size of 0.07～ 0.15 mm,transparent light yellow color,glass luster,brittleness and colorless streak.Its Vickers microhardness is 487～ 583 kg/mm2 （near 5 on the Mohs hardness scale）,its calculated density and N are 7.11 g/cm3 and 2.15 respectively,and its mineral chemical formula is Bi4Si3O12.The strongest reflections in the X-ray powder diffraction pattern [d （A）（I）] are 4.26 （85）,3.29 （100）,2.77（79）,2.11（45） and 1.67（33）,and the unit cell parameters are a =10.116（2） A,V =1 035.2（7） （A）3,and Z =4.The genesis of eulytite is also discussed in this paper.