加热处理镁铝榴石的晶体化学研究

通过应用XRD,IR和MS谱对加热过程中的一个紫红色含铬镁铝榴石样品作了研究,结果表明,在1000℃时,镁铝榴石转化为辉石和非晶态的Al_2O_3,但在加热只达800℃的过程中,其十二面体中的Fe~(2+)逐渐氧化为Fe~(3+),并与四面体中原有的Fe~(3+)和八面体中的Al~(3+)一同析出。从而得出,在镁铝榴石结晶过程中,高温有利于Fe~(3+)和Cr~(3+)取代Al~(3+)进入八面体,但却不利于Fe~(3+)进入四面体。这一结论对重新认识镁铝榴石在金刚石找矿方面的标志特征具有十分重要的意义。

A STUDY ON THE CRYSTAL CHEMISTRY OF A PYROPE GEATED UNDER DIFFERENT TEMPERATURES

The crystal chemistry of a pyrope sample purple in color from a kimberlite in Guizou Province of China heated at different temperatures has been studied with X-ray diffraction, infrared and Mossbauer spectrtum. It's shown that the structure of the pyrope is destroyed thoroughly at 1000C and turns into pyroxene and noncrystalline Al_2O_3. But below 800C, the Fe~(2+) in the dodecahedron of the crystal is being oxidized gradually into Fe~(3+) which then discomposed out of the mineral with the other Fe~(3+) in tetrahedron and Al~(3+) in cotahedron togather by increasing the temperature. So, is the process of the crystalization of pyropes Fe~(3+) will prefer octahedral sites to tetrahedral ones and this will be beneficial to a substitution of Cr~(3+) for Al~(3+) in octahedron at high temperature. This study is of importance for rerealizing its ty- pomorphic characteristics refered to exploration of diamond.