Mineralogical Studies of Carbonatites.

对碳酸盐岩和碱性岩石组成矿物的结构和化学成分进行了研究，主要使用了Monbusho国际科学研究计划“巴西碱性复合体稀土和放射性矿物研究”（首席研究员：Masayasu TOKONAMI教授）获得的标本。主要观察的是以下现象：(1)辉石与碳酸盐接触处的变质作用使辉石蚀变为蛇纹石；(2)不仅从碳酸盐中，而且从硅酸盐、氧化物等中，都有明显的碱金属和碱土金属离子的浸出现象；(3)在单氮石、闪长石等磷矿物中，稀土元素的浓度具有特征性，风化作用使稀土元素富集为横纹石、辉长石、goyazite等。在这个项目中，我们也为微区x射线衍射技术的发展做出了贡献。通过应用这种方法，我们可以在不破坏样品的情况下识别至少5-10 μ m结晶相的矿物。此外，还可以确定在织构中观察到的不同晶相之间的晶图取向关系。因此，该方法将有助于通过光学显微镜、扫描电镜等综合观测，阐明碳质岩浆的凝固及其与碱性岩石的变质作用、风化作用等各种复杂的成矿过程。

Studies on textures and chemical conpositions of constituent minerals of carbonatites and alkaline rocks were performed mainly using specimens obtained by the Monbusho International Scientific Research Program entitled "Studies on rare-earth and radioactive minerals of alkaline complexes in Brasil" (Head Investigator : Professor Masayasu TOKONAMI). Main subjects are the observations of following phenomena : (1) alteration of pyroxene into serpentine by a metamorphism at the contact of jacupirangite with carbonatite, (2) remarkable leaching phenomena of alkaline metal and alkaline-earth metal ions not only from carbonates but also from silicates, oxides, etc., (3) characteristic concentrations of rare-earth elements in such phosphate minerals as monazite, cheralith, etc., and concentrations into rhabdophane, crandallite, goyazite, etc. as a result of weathering.In this project, we also contributed to the development of a microarea X-ray diffraction technique. By applying this method, we can identify minerals up to the minimum of 5-10 mum crystalline phases without destroy of the specimen. Furthermore, it is possible to determine the crystallo-graphic orientation relationship among different crystalline phases which are observed in textures.Thus, this method will contribute to clarify various complicated mineralization processes such as solidification of carbonaceous magmas and its metamorphism with alkaline rocks, weathering processes, etc., by combined observations of an optical microscope, scanning electron microscope, etc..