新矿物中华铈矿Ba2Ce(CO3)3F

新近发现一种含钡和稀土的氟碳酸盐矿物,经电子探针、矿物化学、X-射线粉品、X-射线能谱、电子衍射、扫瞄电予显微镜和透射电子显微镜等分析,偏光显微镜和反光显微镜光性鉴定,差热分析以及显微硬度、比重和其他物理性质测定,确定是一种新矿物。

ZHONGHUACERITE Ba2Ce(CO3)3F——A NEW MINERAL

Recently a new mineral was discovered and identified as a member of barium rare-earth fluor-carbonate mineral series.It is extremely fine grained The aggregated mineral composed of grains is granular.Its aggregate is pale yellowish in colour with a light yellowish streak (powder).There is no cleavage even in the fine aggregate,the cleavage may be not shown.Luster vitreous or greasy,translucent,its microhardness measured as 289-309kg/mm² and the Mohs hardness is approximately 4,6.After its locality and chemical composition we named it Zhonghaucerite Ba₂Ce (CO₃)₃F.Zhonghuacerite is uniaxial (-) with refractive indices ∈=1,568 and ω=1,745.By means of pycometer,its measured density is 4.20-4.40g/cm³ and the calculated density is 4.66/cm³.The chemical composition of three Zhonghuacerite samples,determined by wet chemical analysis,are as follows respectively: BaO 44.26,45.93 and 45.74; CaO,2.33,2.76 and 3.05; SrO,1.79,1.81 and 1.93; MgO,0.85,0.06 and 2.23; Ce₂O₃ 10.96,10.67 and 10.11; (La,Nd.....)₂O₃,13.89,12.23 and 11.91; Fe₂O₃,2.52,2.40 and 1.50;Al₂O₃,0.06,0.16 and 0.08; ThO₂,0.41,0.38 and 0.29; CO₂,21.10 20.98 and 20.77; F,3.21,4.00 and 3.77 percent,sum 101.38.After-O=F₂ they are 100.03,99.70 and 99.80 respectively.The chemical formula of the first sample is (Ba_1.68Ca_0.24Sr_0.08)_2.00(Ce_0.39 Ln_0.50 Fe_0.18 Mg_0.12 Th_0.01 Al_0.01 C_2.79 O_9.33 F_0.95;the second one is (Ba_1.64 Ca_0.27 Sr_0.09)_2.00 (Ce_0.35 Ln_0.41 Fe_0.16 Al_0.02 Mg_0.01 Th_0.01)_0.96 C_2.60 O_8.65 F_1.15;the third one is (Ba_1.64 Ca_0.24 Sr_0.10)_2.00 (Ce_0.33 Ln_0.39 Fe_0.10 Al_0.01 Mg_0.03 Th_0.01)_0.87 C_2.54 O_9.71 F_1.07 or ideally it is Ba₂ RE (CO₃)₃ F.The theoretical composition for the empirical formula of Zhonghuacerite Ba₂ Ce(CO₃) F is (wt%) BaO 49.91,Ce₂O₃ 26.71,CO₂ 21.48,F 3.28,snm 101.38,-O=F₂ 1.38 percent.By electron probe analysis Zhonghuacerite mainly contains cerium among rare earth element.Zhonghuacerite is easily soluble in HC1,H₂SO₄,HNO₃ and HClO₄The mineral is trigonal,and its hexagonal subcell parameters are: a’=5.07Å,c’=9.82Å,v’=218.6ų,Z=1.The d values(Å) of the strongest X-ray diffraction lines and their relative intensities are: 3.92(8),3.419(4),3.216(10),2.512(6),2.123(3),2.103(10),1.979(10),1.638(3),1.572(3).Electron diffraction pattern and X-ray energy spectrum of Zhonghuacerite are quite different from that of similar minerals,such as cordylite,huanghoite,and cebaite,and have its own character.Zhonghuacerite is quite different from huanghoite and cebaite in the differential thermal curves,for example,its first big endothermic effect appears near at 645℃ (decomposion of CO₂),and not at 680°-690℃ as the last two do.Whereas the second big endothermic effect of the three minerals are the same all at 800℃ (BaCO₃ decomposed).Zhonghuacerite was found in the Proterozoic metamorphic dolomite from Bayan Obo in Noth China,and associated with cebaite,ferro-dolomite phlogopite,riebeckite,magnetite and quartz etc.The type specimens are preserved in the Museum of Geology (Beijing).