Crowningshieldite is the natural analog of the synthetic compound α-NiS. It has a NiAs-type structure and is the high-temperature polymorph relative to millerite (β-NiS), with an inversion temperature of 379 °C. Crowningshieldite is hexagonal, space group P63/mmc, with a = 3.44(1) Å, c = 5.36(1) Å, V = 55.0(2) Å3, and Z = 2. It has an empirical formula (Ni0.90Fe0.10)S and dcalc = 5.47(1) g/cm3. The five strongest lines in the powder X-ray diffraction data are [dmeas in angstroms (I) (hkl)]: 1.992 (100) (102), 1.718 (55) (110), 2.978 (53) (100), 2.608 (35) (101), and 1.304 (17) (202). Crowningshieldite was found as part of a multiphase inclusion in a gem-quality, colorless, type IIa (containing less than ~5 ppm N) diamond from the Letseng mine, Lesotho. The inclusion contains crowningshieldite along with magnetite-magnesioferrite, hematite, and graphite. A fracture was observed that extended from the inclusion to the diamond exterior, meaning that fluids, possibly kimberlite-related, could have penetrated into this fracture and altered the inclusion. Originally, the inclusion might have been a more reduced, metallic Fe-Ni-C-S mixture made up of cohenite, Fe-Ni alloy, and pyrrhotite, akin to the other fracture-free, pristine inclusions within the same diamond. Such metallic Fe-Ni-C-S primary inclusions are a notable recurring feature of similar type IIa diamonds from Letseng and elsewhere that have been shown to originate from the sublithospheric mantle.The discovery of crowningshieldite confirms that the α-NiS polymorph occurs in nature. In this case, the reason for its preservation is unclear, but the relatively iron-rich composition [Fe/(Fe+Ni) = 0.1] or the confining pressure of the diamond host are potential factors impeding its transformation to millerite. The new mineral name honors G. Robert Crowningshield (1919–2006) (IMA2018-072).

中文翻译：

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新的矿物冠冕盾晶石：莱索托莱森矿的IIa型钻石中发现的高温NiS多晶型物

皇冠盾矿是合成化合物α-NiS的天然类似物。它具有NiAs型结构，是相对于蒙脱石（β-NiS）的高温多晶型物，转化温度为379°C。冕状盾构体为六边形，空间群为P63 / mmc，a = 3.44（1）Å，c = 5.36（1）Å，V = 55.0（2）Å3，Z =2。它具有一个经验公式（Ni0.90Fe0。 10）S和dcalc = 5.47（1）g / cm3。粉末X射线衍射数据中最强的5条线为[dmeas埃（I）（hkl）]：1.992（100）（102），1.718（55）（110），2.978（53）（100），2.608 （35）（101）和1.304（17）（202）。在莱索托的莱森矿，发现一颗宝石品质，无色的IIa型（含N含量​​小于约5 ppm）钻石为皇冠状盾构多相夹杂物的一部分。夹杂物包括冠状盾岩以及磁铁矿-镁铁素体，赤铁矿，和石墨。观察到一条从夹杂物延伸到钻石外部的裂缝，这意味着可能与金伯利岩有关的流体可能已经渗透到该裂缝中并改变了夹杂物。最初，夹杂物可能是还原性更强的，由钴红铁矿，Fe-Ni合金和黄铁矿组成的金属Fe-Ni-CS混合物，类似于同一颗钻石中的其他无裂纹的原始夹杂物。此类金属Fe-Ni-CS初级夹杂物是莱森（Letseng）和其他地区的类似IIa型钻石的显着重复特征，这些钻石已被证明源自岩下圈地幔。加冕盾晶石的发现证实了α-NiS多晶型物自然存在。在这种情况下，其保存的原因尚不清楚，但是相对富铁的组成[Fe /（Fe + Ni）= 0。1]或钻石主体的围压可能是阻碍其转变为辉石的潜在因素。新的矿物名称授予G. Robert Crowningshield（1919–2006）（IMA2018-072）。