富钛尼日利亚石的发现与研究

富钛尼日利亚石产于燕山早期花岗岩体与泥盆系上统灰岩外接触带的大理岩中,呈六方板状,浅黄到棕黄色,(0001)解理完全,D=4.1,Hv=1280kg/mm~2(荷重50g),弱多色性,低重折率,No>Ne>1.78,一轴(一)。晶体结构为六方晶系,晶胞参数:α=5.7004,c=13.8699,V=390.33~3。探针成分多点分析平均含量:TiO_26.205、SiO_20.191、MgO5.525、MnO1.134、SnO_217.585、Al_2O_358.491、FeO5.021、CaO0.161、ZnO5.619。Kα特征X射线图象表明,钛在矿物中呈均匀分布,与锡成类质同象存在。富钛尼日利亚石是尼日利亚石的新变种。是在富Ti、Sn、高Zn、Al的岩浆期后热液中形成。

THE DISCOVERY OF TITANIUM-RICH NIGERITE

Titanium-rich nigerite has been found for the first time in China. It occurs in marbles in the exo-contact zone between the Yengshanlan biotite granite stock and the Upper Devonian liemstone in Shizhuyuan, Guangxi. As hexagonal plates, it is light yellow to brown-yellow with perfect (0001) cleavage. D=4.1, Hv_(50)=1280kg/mm~2 Uniaxial(-). Refractive indices No>Ne>1.78.Birefringence is low. Crystallographically it is of hexagonal symmetry. Unit cell parameters are a=5.7004, c=13.866, cell volume=390.33(?)~3. Electron microprobe analysis gave average values SnO_2=17.585, Al_2O_3=58.491, FeO=5.021, MGO=5.525, MnO=1.134, ZnO=5.619,TiO_2=6.205, SiO_2=0.191 and CaO=0.161. Ti, probably substituting for Sn, is shown homogeneously distributed in the mineral. The mineral is regarded as a subspecies of nigerite, and is supposed to be formed from postmagmatic hydrothermal fluids rich in Ti, Sn, Zn and Al.