Rhombohedral Structure: A New Phase of Pentlandite in Diamond Inclusion from Liaoning, China
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摘要: 从金刚石中获取的包体矿物经电子探针分析其成分与镍黄铁矿相同, 该包体矿物晶体形态完好, 外形为三(六)方对称.用CCD单晶衍射仪对该矿物进行了单晶德拜衍射, 得到的39个衍射峰, 经粉末法指标化程序判别和计算, 这些衍射峰分别属于两种结构的镍黄铁矿的衍射峰: 一套为菱面体结构(六方定向)镍黄铁矿的衍射; 另一套属于立方结构的镍黄铁矿结构的衍射.菱面体结构镍黄铁矿的晶胞参数: a=0.690 62 nm, c=1.720 95 nm, V=0.710 85 nm3(六方定向); aR=0.698 61 nm, α=59.244 5°, V=0.236 95 nm3(菱面体定向).菱面体结构的衍射表明该镍黄铁矿在地幔超高压环境中形成, 出现立方结构的衍射, 反映了金刚石破碎后, 该镍黄铁矿包体在常压下相变的结果.Abstract: Pentlandite inclusion presenting perfect crystal form with hexagonal symmetry in a diamond from Liaoning of China was confirmed based on electron microprobe analysis data.X-ray diffraction peaks obtained from single crystal diffractometer with CCD area detector demonstrate that pentlandite has rhombohedral and cubic structures by the powder method indexing procedure distinction and computation. Unit cell parameters of rhombohedral structure are as follows: a=0.690 62 nm, c=1.720 95 nm, V=0.710 85 nm3 (hexagonal); aR=0.698 61 nm, α=59.244 5°, and V=0.236 95 nm3 (rhombohedral). The presence of rhombohedral phase in diamond inclusions reveals that the formation condition of the pentlandite in the mantle at ultrahigh-pressure and cubic phase is the results of phase transformation of the pentlandite inclusions in the atmospheric pressure since the diamond breaks.
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Key words:
- rhombohedral structure /
- pentlandite /
- mantle mineral /
- ultra-high pressure /
- diamond inclusion
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表 1 金刚石包体镍黄铁矿的电子探针分析结果(%)
Table 1. Electron microprobe analysis results of pentlandite in diamond inclusion
Fe Ni Co S 合计 计算分子式 Ni/Fe Me/S 1 31.06 34.18 0.44 33.17 98.85 (Ni4.50Fe4.30Co0.06)8.86S8 1.05 8.86/8 2 30.94 34.13 0.49 34.02 99.58 (Ni4.38Fe4.18Co0.06)8.62S8 1.04 8.62/8 3 30.09 34.64 0.48 32.91 99.12 (Ni4.60Fe4.34Co0.06)9.00S8 1.04 9/8 4 30.66 34.84 0.50 33.36 98.24 (Ni4.56Fe4.22Co0.06)8.84S8 1.08 8.84/8 5 30.94 34.11 0.50 32.84 98.40 (Ni4.50Fe4.30Co0.06)8.86S8 1.05 8.86/8 6 32.04 33.52 0.51 33.31 99.38 (Ni4.54Fe4.33Co0.07)8.94S8 1.00 8.94/8 7 31.19 34.45 0.51 32.87 99.01 (Ni4.40Fe4.42Co0.07)8.89S8 1.05 8.89/8 表 2 金刚石包体Ni、Fe硫化物矿物的X射线衍射数据
Table 2. X-ray diffraction data of Ni, Fe sulfide minerals in diamond inclusion
菱面体结构镍黄铁矿衍射峰(本次) 立方结构镍黄铁矿衍射峰(本次) 镍黄铁矿立方PDF 30-657 hkl 计算d(nm) 实验d(nm) Int* hkl d(nm) Int hkl d(nm) Int 111 0.5675 30 111 0.5794 29 003 0.573 65 0.561 30 s 101 0.564 94 0.543 30 m 200 0.510 7 16 200 0.501 8 6 102 0.491 11 0.493 00 s 220 0.354 7 8 220 0.354 8 6 104 0.349 26 0.349 20 m 110 0.345 31 0.341 70 m 111 0.338 56 0.339 40 m 311 0.300 1 91 311 0.302 6 98 222 0.289 9 8 222 0.289 7 29 006 0.286 83 0.286 29 w 202 0.282 47 0.282 74 w 203 0.265 18 0.266 30 w 106 0.258 62 0.259 60 w 400 0.250 97 7 400 0.250 89 5 331 0.227 66 8 331 0.230 31 16 210 0.226 06 0.224 93 w 205 0.225 74 0.223 22 m 420 0.223 22 4 420 0.224 47 3 422 0.205 40 5 422 0.204 92 2 511 0.192 10 30 511 0.193 18 34 009 0.191 22 0.191 39 s 303 0.188 32 0.188 80 m 440 0.175 83 100 440 0.177 43 100 220 0.172 65 0.173 19 w 305 0.172 51 0.171 76 w 221 0.171 79 0.171 33 w 531 0.169 80 15 531 0.169 67 4 600 0.166 80 5 600 0.167 27 1 312 0.162 88 0.163 28 w 209 0.161 10 0.161 14 m 313 0.159 35 0.158 69 w 620 0.157 14 3 620 0.158 69 1 218 0.155 84 0.155 85 w 533 0.153 11 22 533 0.153 09 8 622 0.150 58 20 622 0.151 32 8 444 0.143 96 5 444 0.144 88 1 0012 0.143 41 0.142 60 m 404 0.141 24 0.141 54 m 注:Int*:衍射峰相对强度;s.强;m.中;w.弱. -
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