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

L.黄长石（Melilite）：用浮区法在N.A.的灯像炉上生长了镁黄长石固溶体（Ca，Sr）_2（Mg，Co，Zn，Fe）Si_2O_7单晶。Jb. Miner，MH，1989 - 5，219 - 226，1989）。用电子衍射、晶格象、X射线衍射、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、I-N跃迁和局域结构。Chem.Minerals，17 - 5，467471，1990;同上，17 - 8，720 - 725，1991;同上，提交，1992; Eur. J·迈纳，（1992年）。利用光学衍射方法对调制结构进行了分析。考虑了各原子间的相位关系以及横波和纵波引起的方向卫星，得到了能较好解释观测数据的模型.<110><100>莱呼石莱呼石是一种具有超结构的非化学计量的橄榄石型矿物，是通过在空气中将合成的铁锰橄榄石粉末和单晶在500、600和700 ℃下加热而产生的。结果表明，富铁橄榄石（N。Jb.矿工嗯，1989 - 6，245254，1989）。在300 - 800 ℃的氧分压控制气氛下，通过在空气中加热合成的FO-（Mg，Co，Mn，Ca）橄榄石的粉末和单晶，研究了羊毛石的形成。结果表明，莱芜矿的多晶型（2C，3C_1，3C_2）取决于原始橄榄石（N. Jb.矿工嗯，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).