地幔超高压条件下镍黄铁矿的一种新结构相——菱面体相: 辽宁金刚石包体的镍黄铁矿晶体结构

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); a_R＝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. 

Rhombohedral Structure: A New Phase of Pentlandite in Diamond Inclusion from Liaoning,China

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); a_R＝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.