Structure refinements of coquimbite and paracoquimbite from the Hongshan Cu-Au deposit, NW China

doi:10.1127/ejm/2018/0030-2752

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	Structure refinements of coquimbite and paracoquimbite from the Hongshan Cu-Au deposit, NW China
	Yang, Zhuming 1,2; Giester, Gerald 3
刊名	EUROPEAN JOURNAL OF MINERALOGY
	2018-07-01
卷号	30 期号:4 页码:849-858
关键词	coquimbite paracoquimbite crystal-structure refinement hydrogen bonding formula revision NW China
ISSN号	0935-1221
DOI	10.1127/ejm/2018/0030-2752
英文摘要	The crystal structures of coquimbite and paracoquimbite from the Hongshan Cu-Au deposit, NW China, were refined by single-crystal X-ray diffraction, including the positions of all non-H atoms and hydrogen atoms. The unit-cell parameters of coquimbite are a = 10.9644(15), c = 17.090(3) angstrom, and V = 1769.6(5) angstrom(3), Z = 4 with space group P (3) over bar 1c. The crystal structure was refined based on 1352 unique reflections to R1(F) = 0.0301, yielding the formula Fe1.64Al0.36(SO4)(3)center dot 9H(2)O. Among the three cation positions of coquimbite, the isolated octahedral one is dominantly occupied by Al, i.e. Al0.660(3)Fe0.340(3). Consequently, the average Al-O interatomic distance is 1.9155 angstrom, smaller than the Fe-O distances, 2.002 angstrom for Fe(1), and 1.989 angstrom for Fe(2). Based on the structure data available for coquimbite in the literature, the ideal formula should be expressed as AlFe3(SO4)(6)center dot 18H(2)O (Z = 2) or Fe2-xAlx(SO4)(3)center dot 9H(2)O, x similar to 0.5 rather than Fe-2(3+)(SO4)(3)center dot 9H(2)O. The simplified formula for coquimbite from Hongshan is (Al0.66Fe0.34)Fe-3(SO4)(6)center dot 18H(2)O(4). The unit-cell parameters of paracoquimbite are a = 10.9631(16), c = 51.473(10) angstrom, and V = 5357.7(15) A(3) Z = 12 with space group R (3) over bar. The crystal structure was refined using 2733 unique reflections to R1(F) = 0.0550, which led to the formula Fe1.91Al0.09(SO4)(3)center dot 9H(2)O. There are five non-equivalent octahedrally coordinated metal sites for Fe in the structure of paracoquimbite. The range of Fe-[6]-O interatomic distances in paracoquimbite (1.966 angstrom-2.016 angstrom) can well be compared with those found in various sulfate minerals of ferric iron. Both minerals are characterized by a complex system of hydrogen bonds involving three types of H2O molecules, respectively: those of [Fe-3(SO4)(6) (H2O)(6)](3) clusters, of isolated [Fe(H2O)(6)](3+) or [Al(H2O)(6)](3+) octahedra and further interstitial (H2O) groups. The interstitial H2O molecules resemble a cyclohexane-like chair and are held in the structure solely by hydrogen bonding. In coquimbite H(2)Ow(2) is disordered with two alternative orientations (H2B1 and H2B2), in paracoquimbite interstitial H2O consists of two H2O molecules, H(2)Ow(3) and H(2)Ow (4). The range of the O-H stretching frequencies between similar to 2750 and 3650 cm(-1) from infrared spectroscopy for paracoquimbite is in fair accordance with the calculated values between similar to 2874 and similar to 3600 cm(-1) from both the d(O center dot center dot center dot O) lengths and the d(H center dot center dot center dot O) lengths.
资助项目	National Natural Science Foundation of China[41272063]
WOS关键词	HYDRATED FERRIC SULFATES ; CRYSTAL-STRUCTURE ; MINERAL CHEMISTRY ; EASTERN TIANSHAN ; BOND-VALENCE ; PROVINCE
WOS研究方向	Mineralogy
语种	英语
出版者	E SCHWEIZERBARTSCHE VERLAGSBUCHHANDLUNG
WOS记录号	WOS:000449622000017
资助机构	National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China ; National Natural Science Foundation of China
内容类型	期刊论文
源URL	[http://ir.iggcas.ac.cn/handle/132A11/89437]
专题	地质与地球物理研究所_其他部门
通讯作者	Giester, Gerald
作者单位	1.Chinese Acad Sci, Inst Geol & Geophys, Beijing 100029, Peoples R China 2.Chinese Acad Sci, Inst Earth Sci, Beijing, Peoples R China 3.Univ Wien, Inst Mineral & Kristallog, Althanstr 14, A-1090 Vienna, Austria
推荐引用方式 GB/T 7714	Yang, Zhuming,Giester, Gerald. Structure refinements of coquimbite and paracoquimbite from the Hongshan Cu-Au deposit, NW China[J]. EUROPEAN JOURNAL OF MINERALOGY,2018,30(4):849-858.
APA	Yang, Zhuming,&Giester, Gerald.(2018).Structure refinements of coquimbite and paracoquimbite from the Hongshan Cu-Au deposit, NW China.EUROPEAN JOURNAL OF MINERALOGY,30(4),849-858.
MLA	Yang, Zhuming,et al."Structure refinements of coquimbite and paracoquimbite from the Hongshan Cu-Au deposit, NW China".EUROPEAN JOURNAL OF MINERALOGY 30.4(2018):849-858.