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常温下,顽火辉石(MgSiO)_■)有两种稳定相,即正交顽火辉石(O)和单斜顽火辉石(C)。两相之间的取向关系为(100)_o∥(100)_c、[001]_0∥[001],可形成沿[100]方向的共格连生体。利用高分辨电镜观察了吉林陨石中的顽火辉石及产于不同地质条件下的其它四种岩体中顽火辉石的多型结构,并对它们中的多型现象进行比较。发现陨石中的多型现象最为明显.其中单斜结构区域在a方向上的宽度多数为a_c·Sinβ=9A的奇数倍。而且相邻的单斜结构区域呈孪晶关系;与此相反,岩体中单斜结构出现的频率较低。多数区域宽度为9A的偶数倍。并且无孪晶关系。据此讨论了它们的多型现象产生原因:吉林陨石中的顽火辉石主要经历了高温急冷过程,在这个过程中原顽火辉石生成正交和单斜顽石多型体。
At room temperature, enstatite (MgSiO) _ ■ has two stable phases, orthorhombic pyroxene (O) and monoclinic enstatite (C). The orientation relationship between the two phases is (100) _o // (100) _c, [001] _0∥ [001], forming coherent bodies along the [100] direction. The pyrrhotite in Jilin meteorite and the polytype structure of enstatite in the other four kinds of rocks under different geological conditions were observed by high resolution electron microscope, and their multi-type phenomena were compared. It is found that the polytype phenomenon in meteorites is most obvious, in which the width majority of the monoclinic region in a direction is an odd multiple of a_c · Sinβ = 9A. In addition, the adjacent monoclinic structures are twinned; in contrast, the occurrence of monoclinic structures in rock mass is lower. Most area width is an even multiple of 9A. And no twins. Based on this, the reasons for their multi-type phenomena are discussed. The enstatite in Jilin meteorite mainly undergoes the high-temperature rapid cooling process, in which the protolith pyroxenes produce orthorhombic and monoclinic multiphase.