The crystal structure of (Fe_(4)Cr_(4)Ni)_(9)C_(4)  

作　　者：SHI Nicheng1, MA Zhesheng1, XIONG Ming1, DAI Mingquan1, BAI Wenji2, FANG Qingsong2, YAN Binggang2 & YANG Jingsui2 1. X-ray Diffraction Laboratory, China University of Geosciences, Beijing 100083, China 2. Institute of Geology, Chinese Academy of Geological Sciences, Beijing 100037, China 

出　　处：《Science China Earth Sciences》2005年第3期338-345,共8页中国科学（地球科学英文版）

基　　金：supported by the National Natural Science Foundati on of China(Grant Nos.4024201 3 and 40472075)

摘　　要：(Fe4Cr4Ni)9C4 is a metal carbide mineral formed by combination of Fe, Cr and Ni with C. It occurs in a chromite deposit in the Luobusha ophiolite, Tibet. Based on the determina- tion of its crystal structure, the empirical formula is (Fe4.12Cr3.84Ni0.96)8.92C3.70 and the simplified formula is (Fe4Cr4Ni)4C9. The mineral is hexagonal with a = 1.38392(2) nm, c = 0.44690(9) nm, space group P63 m c, Z=6 and the calculated specific gravity Dx = 7.089 g/cm3. Fe, Cr and Ni occupy different crystallographic sites and their coordination numbers are approximately 12, forming an alternate stacking sequence of flat and puckered layers along the c axis. Some me- tallic atoms have a defect structure. The interatomic distances of Fe, Cr and Ni are 0.2525— 0.2666 nm, and the distances between Fe, Cr, Ni and C are 0.1893—0.2169 nm. The coordina- tion number of carbon is 6. It occurs in interstices of the metallic atoms Fe, Cr and Ni to form trigonal-prismatically coordinated polyhedra. These coordination polyhedra are linked with each other via shared corners or shared edges into a new type of metal carbide structure.(Fe4Cr4Ni)9C4 is a metal carbide mineral formed by combination of Fe, Cr and Ni with C. It occurs in a chromite deposit in the Luobusha ophiolite, Tibet. Based on the determina- tion of its crystal structure, the empirical formula is (Fe4.12Cr3.84Ni0.96)8.92C3.70 and the simplified formula is (Fe4Cr4Ni)4C9. The mineral is hexagonal with a = 1.38392(2) nm, c = 0.44690(9) nm, space group P63 m c, Z=6 and the calculated specific gravity Dx = 7.089 g/cm3. Fe, Cr and Ni occupy different crystallographic sites and their coordination numbers are approximately 12, forming an alternate stacking sequence of flat and puckered layers along the c axis. Some me- tallic atoms have a defect structure. The interatomic distances of Fe, Cr and Ni are 0.2525— 0.2666 nm, and the distances between Fe, Cr, Ni and C are 0.1893—0.2169 nm. The coordina- tion number of carbon is 6. It occurs in interstices of the metallic atoms Fe, Cr and Ni to form trigonal-prismatically coordinated polyhedra. These coordination polyhedra are linked with each other via shared corners or shared edges into a new type of metal carbide structure.

关 键 词：LUOBUSHA of Tibet  METAL carbide  CRYSTAL structure. 

分 类 号：P618.2[天文地球—矿床学]