Crystal Chemistry Research of Minerals of Nigerite Group and Its Significance

There is a type of complex oxide mineral, composed of many elements such as Sn, Mg, Fe, Zn, Ti, Mn, Al, etc., in the areas of Anhua, Linwu and Shizhuyuan of Hunan Province. These minerals belong to nigerite, Mg-nigerite （pengzhizhongite）, etc.. According to the principle of closest packing, the crystal chemical properties of nigerite （brown）, pengzhizhongite （buff）, Zn-nigerite （fawn）, Fe-nigerite, Mn-nigerite （greenish-black） etc. have been analyzed. Their crystal structures may be characterized by O （the layers of cation octahedral coordinations）, T1 （the mixed layers of cation octahedral coordinations and cation tetrahedral coordinations in same directions）, T2 （the mixed layers of cation octahedral coordinations and cation tetrahedral coordination in different directions）. The position of layer-O and layer-T is alternate permutation. The crystal structure of pengzhizhongite （6 H ） may be expressed by …OT2OT1OT1…, taaffeite （8 H ）, …OT2OT1OT2OT1…, and nigerite （24 R ）, … OT1OT2 OT2OT1 …×3 etc.. In their structure, there are not only the crystal structure units of spinel … OT2 OT2 … but also the units of nolanite … OT1 OT1 …. The research of these minerals has important theoretic and practical significance in the fields of minerals, gemology, material science etc..

尼日利亚石类矿物的晶体化学研究及其意义

湖南省安化、临武、柿竹园等地区有一类含锡、镁、铁、锌、钛、锰、铝等多种元素的复杂氧化物矿物 ,它们是尼日利亚石、镁尼日利亚石 (彭志忠石 )等。本文从紧密堆积原理出发 ,深入探讨了尼日利亚石类矿物的晶体化学特征。它们的晶体结构可用O(阳离子八面体配位的层 )、T1(阳离子八面体配位与一种方向阳离子四面体配位的混合层 )、T2 (阳离子八面体配位与两种方向阳离子四面体配位的混合层 )堆积方式表征 ,O层与T层交替排列。尼日利亚石 6H的晶体结构表示为…OT2 OT1OT1… ,尼日利亚石 2 4R的晶体结构表示为…OT1OT2 OT2 OT1…× 3 ,等等 ;它们的晶体结构中既有尖晶石的…OT2 OT2 … ,又有铁钒矿的…OT1OT1…晶体结构单位。这类矿物研究在矿物学、宝石学。