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曲面金刚石广泛产于金刚石砂矿和含金刚石的金伯利岩管及钾镁煌斑岩中。曲面金刚石是一种特殊的晶体类型 ,它与平坦面金刚石相比 ,不仅晶习不同 ,曲面金刚石常呈四六面体 ,而平坦面金刚石常呈八面体 ,而且它更坚实 ,更具宝石价值。热力学计算和实验表明 ,八面体金刚石比立方八面体和立方体金刚石的形成温度高 ,意味着曲面金刚石形成深度较浅 ,可能在石墨 -金刚石稳定区的边界上。目前对曲面金刚石是生长形还是由平坦面金刚石熔蚀而成尚有不同见解。文章对俄罗斯地台北缘和东北缘的曲面金刚石进行了综合研究。经切割抛光 ,用 X射线形貌法、阴极发光法和普通光学法进行了结构研究 ,还对金刚石进行了光学荧光、 X射线荧光 ( T=77～ 2 90 K)、ESR电子自旋共振、可见光区的吸收谱等研究。用光学测角仪和扫描电镜查明 ,研究区的金刚石中四六面体单形占 60 %～ 80 %、 { 0 65} +{ 365} +{ 1 1 1 }聚形占 8%～35%、平坦面八面体占 0～ 8%且无菱形十二面体。研究发现金刚石表面覆有成分不同的薄膜 ,厚约 0 .1～ 1 μm,其成分有 2 9种之多。表明天然金刚石是在多种金属和碳的熔体中结晶的 ,乌拉尔 -巴西型金刚石的曲面晶为生长晶而非熔蚀晶。在罗蒙诺索夫金伯利岩管中获取的金刚石表面附有超基性岩的原生矿物组合?
Surface diamonds are widely produced in diamond sands and diamond-bearing kimberlite tubes and porphyrite. Curved diamond is a special kind of crystal. Compared with flat diamond, not only the crystal habit is different, the curved diamond is usually tetrahedron, while the flat diamond is usually octahedron, and it is more solid and gemstone value. Thermodynamic calculations and experiments show that the formation temperature of octahedral diamond is higher than that of cubic octahedron and cubic diamond, which means that the surface diamond is formed to a shallow depth, possibly at the boundary of graphite-diamond stable zone. There are different opinions about whether diamonds on the surface are in the form of growth or from the erosion of flat diamonds. The article made a comprehensive study of the curved diamonds in the northern and northeastern margin of Russia. The structure of the diamond was studied by X-ray topography, cathodoluminescence and ordinary optical methods. The optical fluorescence, X-ray fluorescence (T = 77-290 K), ESR electron spin resonance Visible light absorption spectrum and other research. It was found by optical goniometer and scanning electron microscope that the hexagonal monofilaments accounted for 60% ~ 80% in the diamonds in the study area, and the {065} + {365} + {1 1 1} polygons accounted for 8% ~ 35% Flat face octahedron 0 to 8% and no diamond dodecahedron. The study found that the surface of diamond coated with different composition of the film, a thickness of about 0.1-1 μm, the composition of 29 as much. It shows that natural diamond is crystallized in the melt of various metals and carbons, while the Ural-Brazilian diamond has grown crystals rather than eroded crystals. The primary mineral assemblage of ultramafic rocks attached to the diamond surface acquired in Lomonosov kimberlite tubes?