【摘要】 新矿物汉江石的理想分子式为Ba2CaV23+[(Si3AlO10)(OH)2]F(CO3)2。矿物呈黄绿色、深绿色,显微镜下呈浅绿色、淡绿色;单斜晶系,空间群为C2,a=0.52050(12)nm,b=0.9033(2)nm,c=3.2077(8)nm,β=93.49(8)°,V=1.5054(8)nm3,Z=4;二轴晶,正延性,负光性,一组完全解理,干涉色为三级绿,多色性明显,浅绿色-黄绿-深绿色;折射率α=1.615,β=1.655,γ=1.700(589 nm),2Vobs=114°～115°,2Vcalc=88.8°;显微硬度平均值203 kg/mm2,相当于莫氏硬度4;实测密度平均3.69 g/cm3,计算密度3.78 g/cm3。X射线粉晶衍射的强谱线有1.5866 nm(7)(002)、0.5340 nm(91)(006)、0.4010 nm(10)(ī14)、0.3209 nm(23)(027)、0.2676 nm(100)(ī110)、0.2294 nm(29)(ī37)和0.2008 nm(11)(228)。汉江石的晶体结构由硅酸盐结构单元TOT(二八面体型)和碳酸盐结构单元Ba2Ca(CO3)2F交替组成,可能有3个多型,即1M型,2M型和3T型。更多还原

【Abstract】 Hanjiangite,a new mineral for the ideal formula Ba2Ca(V3+Al)[Si3AlO10(OH)2]F(CO3)2,is found in the Shiti barium deposit in the Dabashan region,China.Hanjiangite was collected from lenticular witherite ore bodies and witherite-barite-quartz veins cutting carbonaceous slates.It is found as disseminations in both settings.It occurs as thin,euhedral,tetragonal,tabular crystals and anhedral grains.Grain size commonly varies from 0.05 to 4 mm and occasionally reaches 15 mm.It is yellow-green or dark-green,with one well-developed or perfect cleavage on {001}.Other physical properties are: brittle,transparent to translucent,nonfluorescent,vitreous luster,greenish white streak,hardness 4 in Mohs’ scale,splintery fracture,and a measured density of 3.69 g/cm3.Hanjiangite is biaxial(-),α=1.615,β=1.655,γ= 1.700(589 nm),displays strong pleochroism from pale yellow-green to dark green.It is monoclinic,with unit-cell parameters refined by using single-crystal X-ray diffraction:a=5.2050(12),b=9.033(2),c=32.077(8) ,β = 93.49(8)°,V = 1505.4(8)3,Z=4,space group C2.The strongest seven lines of the X-ray powder-diffraction pattern [d in (I)(hkl)]are∶15.866(7)(002),5.340(91)(006),4.010(10)(ī14),3.209(23)(027),2.676(100)(ī110),2.294(29)(ī37),and 2.008(11)(228).A single-crystal X-ray structure determination(sample 2005st-17) was carried out with a Smart APEX CCD system using MoKα(λ = 0.71073 ) radiation.The structure was solved using direct methods,and the refinement conducted with the SHELXTL PC(Bruker AXS Inc.) package of computer programs.Anisotropic refinement using all measured independent data and reflections with I>2σ(I) resulted in an R1 factor of 0.08 and wR2 of 0.20.The crystal structure is composed of alternating T-O-T and Ba2Ca(CO3)2F layers.The Ba2Ca(CO3)2F layer occurs between the T-O-T layers.The T site contains both Si and Al,and the O site both V3+ and Al.The difference is observed in the interlayer,where instead of only Ba(like in chernykhite) there are also Ca atoms and (CO3) groups.Whereas the coordination of the cations in TOT layer are obvious;the coordinations of Ca and Ba in the interlayer are not obvious and not completely different.A hanjiangite has possibly three polytypes,namely 1M-type,2M-type,and 3T-type.更多还原