针状白云母的发现及其成因探讨

针状白云母产于新疆科科托海附近辉长岩－闪长岩内含稀有元素的3号伟晶岩脉中，呈针状或纤维丝状产出，长短轴之比一般大于1：80，最大达1：500。它的晶体结构、化学组成、物理和光学性质与普通白云母相同或类似，属于普通白云母。依据针状白云母产出的地质构造环境和与剪切裂隙的关系，笔者认为针状白云母可能是结晶粗大的白云母在其形成过矿中和形成以后受到垂直于（001）晶面压应力作用，产生三组微裂隙，并沿其中一组发育完全的微裂隙裂开而成。

THE DISCOVERY AND GENETIC INVESTIGATION OF ACICULAR MUSCOVITE

The acicular muscovite occurs in the REE-bearing No. 3 pegmatite vein in the gabbro-diorite massif near Koktokay, Xinjiang and it is present in the form of acicular or fibrous crystals with the ratio of the long axis to the short one genelally being 1: 8 (the maximum500). The crystal structure, chemical composition, physical properties and optical features of the acicular muscovite studied are the same as, or similar to, those of ordinary muscovite. in the light of the relationship between the geotectonic setting of the acicular muscovite and shear-induced faults, the author considers that the formation of the acicular muscovite is the result of a compression perpendicular to (001) of coarse Crystals of muscovite during, or after, its crystallization, leading to the development of three sets of microcracks, along the best developed of which schistose muscovite was broken into acicular or fibrous muscovite as what is observed at present.