Crystal structure and stabilization mechanism of minerals with modulated structure-melilite and Laihunite.

利用灯象炉（N.），采用浮区法生长了黑石固溶体单晶（Ca, Sr）_2(Mg, Co, Zn, Fe)Si_2O_7。简森-巴顿。米纳，Mh, 1989-5, 219-226, 1989)。采用电子衍射法、点阵成像法、x射线衍射法、热容测量、介电常数测量和EXAFS(PH)ys等方法研究了它们的调制结构、非公度-正态（I-N）跃迁和局部结构。化学。矿产，17-5,467471,1990；同上，17-8,720-725,1991；同上，1992年提交；欧元。j .矿工。， 1992年提交)。利用光学衍射法对调制结构进行了分析。考虑了各原子之间的相位关系以及引起<110>方向的卫星的横波和引起<100>方向的卫星的纵波，得到了较好地解释观测数据的模型。莱钙石是一种具有上部结构的非化学计量型橄榄石矿物，由合成Fe-Mn橄榄石的粉末和单晶在500、600和700 <s:1>℃的空气中加热而成。结果表明，由富铁辉石组成的橄榄石形成的莱胡石的空位和三价阳离子少于由富铁辉石组成的橄榄石(N。简森-巴顿。矿工。Mh., 1989-6, 245254, 1989)。在300-800ºC的可控氧分压气氛下，将合成的FO-(Mg, Co, Mn, Ca)橄榄石粉末和单晶加热，研究了其形成过程。结果表明，稀土的多晶型（2C, 3C_1, 3C_2）与原橄榄石(N。简森-巴顿。矿工。Mh., 1989- 8,345 -356, 1989)。

l. MeliliteSingle crystals of akermanite solid-solution, (Ca, Sr)_2(Mg, Co, Zn, Fe)Si_2O_7, were grown by the floating zone method using a lamp-image furnace(N. Jb. Miner, Mh., 1989-5, 219-226, 1989). The modulated structure, the incommensurate-normal(I-N)transition and the local structure of them were studied by the electron diffraction method, the lattice image method, the X-ray diffraction method, the heat capacity measurement, the dielectric constants measurement and the EXAFS(PH)ys. Chem. Minerals, 17-5, 467471, 1990 ; ibid, 17-8, 720-725, 1991 ; ibid, submitted, 1992 ; Eur. J. Miner., submitted, 1992). The analysis of the modulated structure was performed by the optical diffraction method. The model explaining well the observed data was obtained by considering the phase relation among each atoms and both the transverse wave causing the satellites of<110>direction and the longitudinal wave causing the satellites of<100>direction.2. LaihuniteLaihunite, a nonstoichiometric olivine-type mineral with superstructure, has been produced by heating powders and single crystals of synthetic Fe-Mn olivines in air at 500, 600 and 700ﾟC. It was shown that the vacancies and trivalent cations of laihunite formed from tephroite component rich olivine are less than those formed from fayalite component rich olivine(N. Jb. Miner. Mh., 1989-6, 245254, 1989). The formation of lanunite has been examined by heating powders and single crystals of syntheic FO-(Mg, Co, Mn, Ca)olivines in air and under- a controlled atmosphere of oxygei)partial pressure at 300-800ﾟC. It was found that the polymorph(2C, 3C_1, 3C_2)of laihunite depends on the composition of the original olivine(N. Jb. Miner. Mh., 1989-8, 345-356, 1989).