Structural variation of babingtonite depending on cation distribution at the octahedral sites
Structural variation of babingtonite depending on cation distribution at the octahedral sites
复制标题
巴铜矿的结构变化取决于八面体位点的阳离子分布
DOI：
10.1007/s00710-013-0297-z
复制
发表时间：
2014
影响因子：
1.8
通讯作者：
M.
中科院分区：
文献类型：
--
作者：
Nagashima;M.;Mitani;K.;and Akasaka;M.
Babingtonite, Ca2Fe2+Fe3+[Si5O14(OH)] （Z= 2，空间群）来自Yakuki矿（日本），Grönsjöberget（瑞典），Kandivali采石场（印度），Baveno采石场（意大利），bramatstad矿（挪威）和Kouragahana（日本），锰Babingtonite， Ca2(Mn2+, Fe2+)Fe3+[Si5O14(OH)]；采用电子探针分析（EMPA）、57Fe Mössbauer分析和单晶x射线衍射等方法，对美国铁帽矿（Iron Cap mine）样品进行了研究，确定了M1和M2处阳离子的分布，并分析了阳离子对巴宾顿石晶体结构的影响。虽然所有研究的巴彬碳石晶体都是相对均匀的，但在锰巴彬碳石中观察到主要由铁↔锰取代引起的化学分带。Mössbauer光谱由两个双偶体组成，同分异构体位移(I.S.) = 1.16 ~ 1.22 mm/s，四极分裂(Q.S.) = 2.33 ~ 2.50 mm/s， I.S.= 0.38 ~ 0.42 mm/s, q.s = 0.82 ~ 0.90 mm/s，分别分配给M1和M2八面体位置的Fe2+和Fe3+。锰巴菱石中Fe2+/总铁的测定比（0.26）小于其他样品（0.35 ~ 0.44），这是由于锰巴菱石中Mn2+含量高，而非Fe2+。铁灰石的晶胞参数= 7.466 - -7.478,b = 11.624 - -11.642, c = 6.681 - -6.690,α= 91.53 - -91.59,β= 93.86 - -93.94,γ= 104.20 - -104.34º,andV = 560.2 - -562.3 A3和manganbabingtonite面积= 7.4967 (3),b = 11.6632 (4), c = 6.7014(2),α= 91.602(2),β= 93.989(2),γ= 104.574(3)º,andV = 565.09 (5) A3。结构改进的tor1值为1.64 - 3.16%。由于大的八面体阳离子（如Mn2+）取代了Fe2+，使得距离延长。M1-O8、M1-O8′和M1-O13长度随平均离子半径的增加比其他M1-O8长度的增加略明显。M1-O13距离的延长导致Si5-O15-Si1角与M1-O13距离呈正相关。由于M2的平均离子半径增大，Si2-O3-Si1和Si5-O12-Si4的角也增大。
Babingtonite, Ca2Fe2+Fe3+[Si5O14(OH)] (Z= 2, space group) from Yakuki mine (Japan), Grönsjöberget (Sweden), Kandivali Quarry (India), Baveno Quarry (Italy), Bråstad Mine (Norway), and Kouragahana (Japan), and manganbabingtonite, Ca2(Mn2+, Fe2+)Fe3+[Si5O14(OH)], from Iron Cap mine (USA) were studied using electron-microprobe analysis (EMPA),57Fe Mössbauer analysis and single-crystal X-ray diffraction methods to determine the cation distribution at M1 and M2 and to analyze its effect on the crystal structure of babingtonite. Although all studied babingtonite crystals are relatively homogeneous, chemical zonation due to mainly Fe ↔ Mn substitution is observed in manganbabingtonite. Mössbauer spectra consist of two doublets with isomer shift (I.S.) = 1.16–1.22 mm/s and quadrupole splitting (Q.S.) = 2.33–2.50 mm/s and withI.S.= 0.38–0.42 mm/s andQ.S.= 0.82–0.90 mm/s, assigned to Fe2+and Fe3+at the M1 and M2 octahedral sites, respectively. The determined ratio of Fe2+/total Fe in manganbabingtonite (0.26) was smaller than that in the others (0.35–0.44) because of high Mn2+content instead of Fe2+. The unit-cell parameters of babingtonite area= 7.466–7.478,b= 11.624–11.642,c= 6.681–6.690 Å,α= 91.53–91.59,β= 93.86–93.94,γ= 104.20–104.34º, andV= 560.2–562.3 Å3, and those of manganbabingtonite area= 7.4967(3),b= 11.6632(4),c= 6.7014(2) Å,α= 91.602(2),β= 93.989(2),γ= 104.574(3)º, andV=565.09(5) Å3. Structural refinements converged toR1values of 1.64–3.16 %. The distance was lengthened due to the substitution of large octahedral cations such as Mn2+for Fe2+. The increase of the M1-O8, M1-O8’ and M1-O13 lengths with mean ionic radii is slightly more pronounced than of the other M1-Oilengths. The lengthened M1-O13 distance leads the positive correlation between Si5-O15-Si1 angle and M1-O13 distance. The increase of Si2-O3-Si1 and Si5-O12-Si4 angles due to the increase of mean ionic radius of M2 is also observed.